Banishment of Hagar and Yishmael/2

Banishment of Hagar and Yishmael

Exegetical Approaches

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Yishmael's Evil Conduct

Sarah's actions were motivated by the wickedness of Yishmael and a desire to protect Yitzchak from his bad influence.

Sources:ToseftaSotah 5:7About the Tosefta, R. Akiva, R. Elazar b. R. Yosi HaGelili, R. Yishmael, and R. Levi in ToseftaSotah 6:3About the Tosefta, Sifre Devarim6:4About Sifre Devarim, and Bereshit Rabbah53:11About Bereshit Rabbah, Shemot Rabbah1:1About Shemot Rabbah, TanchumaShemot 1About the Tanchuma, Targum Pseudo-JonathanBereshit 21:9-17About Targum Pseudo-Jonathan, Pirkei DeRabbi Eliezer30About Pirkei DeRabbi Eliezer, RashiBereshit 21:9-11,14-15,17About R. Shelomo Yitzchaki, R. Avraham b. HaRambamBereshit 21:9-12Bereshit 21:14Bereshit 21:20About R. Avraham Maimonides, RambanBereshit 21:9-11Bereshit 21:15About R. Moshe b. Nachman, R. Yosef ibn KaspiTirat Kesef pp. 98-99Bereshit 21:9About R. Yosef ibn Kaspi, R. D"Z HoffmannBereshit 21:9-10Bereshit 21:11-13Bereshit 21:14About R. David Zvi Hoffmann¹

"מְצַחֵק" – Although all these sources assume that Yishmael's behavior was reprehensible, they disagree regarding what action is referred to by the term "מְצַחֵק":

• Cardinal sins – According to most of these commentators, the word refers either to idolatry,² murder,³ or illicit relations,⁴ the three cardinal sins in Judaism.⁵
• Sin of speech – Ramban and R. D"Z Hoffmann assert that Yishmael was mocking Yitzchak and the party, while Ibn Kaspi posits that he was poking fun at Sarah.⁶  In contrast, R. Avraham b. HaRambam maintains that Yishmael was more generally fooling around and speaking with a foul mouth.⁷

Banishment – According to this approach, the decision to banish Yishmael stemmed directly from his behavior and "‎צחוק":‎⁸ 

• Spiritual protection – According to most of these sources,⁹ Sarah believed that Yishmael needed to be expelled to ensure that Yitzchak did not learn from his negative ways.  R. Avraham b. HaRambam explains that Sarah feared that she and Avraham might die while Yitzchak was still young, leaving him to grow up under the sole influence of Yishmael, with no counter role models.
• Physical protection – R. Levi, Rashi, and Pirkei deR. Eliezer all maintain that Yishmael had attempted to kill Yitzchak.  As such, Yishmael's banishment was also necessary to physically protect Yitzchak.
• Punishment – In contrast to the above, Ramban views the banishment as a punishment to Yishmael.  He maintains that Sarah viewed Yishmael's actions as a forgetting of his rightful place as servant. Though this normally would deserve death or corporal punishment, Sarah decided instead to expel him.

Disinheritance

• Monetary inheritance – According to most of these commentators, Yishmael's deeds made him unworthy of benefiting from Avraham's wealth.  Alternatively, the disinheritance might have simply been a by-product of the expulsion.
• Spiritual inheritance – R. Avraham b. HaRambam, in contrast, maintains that Sarah was not referring to a monetary inheritance¹⁰ but to a spiritual one.  He asserts that Sarah's words "לֹא יִירַשׁ" are equivalent to the term "גָּרֵשׁ", and simply mean that Yishmael should not live with and be raised by the family.  While Yitzchak was to be educated to religious perfection, Yishmael was to leave and not to join in such an upbringing.

Why is Avraham "upset about his son"? These commentators disagree on this point:¹¹

• Yishmael's behavior – Shemot Rabbah and Targum Pseudo-Jonathan¹² suggest that Avraham was upset that Yishmael had veered from the right path. 
• Yishmael's banishment – Rashi, R. Avraham b. HaRambam, Ramban,and R. D"Z Hoffmann, in contrast, maintain that Avraham was upset about the expulsion and fate of his son.¹³  Ramban suggests that Avraham's natural love for his son made it painful for him to banish him. Although Yishmael's actions were wrong, they were not so terrible to prevent his anguish.¹⁴ R. Avraham b. HaRambam instead claims that Avraham was unaware of Yishmael's true nature,¹⁵ while R. D"Z Hoffmann presents Avraham as hoping to educate Yishmael to become worthy of Hashem's promises.

Why is also Hagar expelled? Ramban asserts that Hagar was sent away due to no fault of her own but out of mercy to Yishmael who would not survive without his mother.

Why does Hashem side with Sarah? For most of these commentators, who claim that Yishmael was guilty of heinous crimes, Hashem's words are not surprising.  The others¹⁶ would likely posit, as does R. Avraham b. HaRambam, that Hashem agreed with Sarah that Yishmael would be a negative influence on Yitzchak.

"לֶחֶם וְחֵמַת מַיִם" – were there sufficient provisions?

• Meager Provisions – Many of these commentators assume that Avraham only scantily provided for Yishmael, but still maintain that the lack of water was not his fault:
• Yishmael got sick – According to Shemot Rabbah and Rashi, Avraham intentionally sent Yishmael away without any gold or silver since he was upset at his sinful ways.  Rashi claims that, nonetheless, he had provided Hagar with ample food and drink.  The water ran out only because Yishmael got sick and drank more than expected.
• Yishmael/Hagar punished – According to Targum Pseudo-Jonathan and Pirkei DeRabbi Eliezer, too, the water supply should have been sufficient¹⁷ but as soon as Hagar entered the wilderness, she strayed after idolatry¹⁸ and was punished.¹⁹
• Avraham obeyed Hashem – R. Avraham b. HaRambam asserts that Avraham's apparent stinginess should not be viewed as such but rather as obedience to the Divine command to listen to his wife.  Moreover, Avraham trusted in Hashem's promise that he would not forsake Yishmael.
• Lessons from need – R. D"Z Hoffmann uniquely suggests that Avraham intentionally did not send Yishmael away with sufficient water.  He recognized that Yishmael needed to learn through trials to look up to Hashem. Perhaps the lack in the desert could teach him the lessons that he was unable to learn in the wealthy home of Avraham.
• Properly provided for – In contrast to the above, Ibn Kaspi maintains that Avraham gave Hagar and Yishmael not only food, but also gold and silver.  He disagrees that Hashem's directive to heed Sarah's words need refer to leaving Yishmael empty-handed.²⁰

Why does Hashem save Yishmael? Targum Pseudo-Jonathan emphasizes that Hashem saved Yishmael only for the sake of Avraham and his merits.²¹

Was Sarah justified?

• Many of these sources justify Sarah's decision by painting a much blacker picture of Yishmael than a simple reading of the text would imply.  Others do so by highlighting the threat he presented to Yitzchak's upbringing.
• R D"Z Hoffmann suggests that Sarah's actions were necessary, but nonetheless caused others pain.  The Torah paints a very sympathetic portrait of Hagar and Yishmael to teach that despite the correctness of Sarah's actions, the banished pair are also worthy of mercy.

Yishmael after the expulsion

• R. Avraham b. HaRambam asserts that Yishmael's becoming an archer, or a man of war, confirmed Sarah's evaluation of his negative character and her worries over how this might affect Yitzchak.
• Rashi and others present Yishmael as repenting at the end of his life.

Avraham's later relationship with Hagar and Yishmael – Pirkei deRabbi Eliezer presents Avraham as concerned about Yishmael's spiritual well-being even after the banishment,²² and has him remarry Hagar after Sarah's death.²³

Ensuring Yitzchak's Inheritance

Sarah acted to ensure that Yitzchak, rather than Yishmael, inherited Avraham's mantle and worldly possessions.

Sources:Rashbi's opinion in the ToseftaSotah 6:3About the Tosefta, Sifre Devarim6:4About Sifre Devarim, and Bereshit Rabbah53:11About Bereshit Rabbah, ²⁴ RadakBereshit 21:9-11,14About R. David Kimchi, RalbagBereshit Beur HaParashah 21:8-16About R. Levi b. Gershom, AbarbanelBereshit 21About R. Yitzchak Abarbanel, SefornoBereshit 21:9-10Bereshit 21:14About R. Ovadyah Seforno, ShadalBereshit 21:9About R. Shemuel David Luzzatto,

"מְצַחֵק" – All of these commentators relate Yishmael's "צחוק" to his desire or likelihood to inherit, but they differ in their interpretations of the word "מְצַחֵק" and the specifics of the incident:

• Mockery – R. Shimon b. Yochai,²⁵ Radak,²⁶ Ralbag, and Shadal²⁷ all portray Yishmael as scorning the concept that Yitzchak alone was to inherit.  Seforno further depicts Yishmael as laughing and spreading rumors that Yitzchak was born of Avimelekh which would thereby disqualify him from inheriting.²⁸
• Playing – Abarbanel, in contrast, understands "מְצַחֵק" to mean play (משחק) and presents Yishmael as happily playing while those around him try to please and serve him. This made Sarah realize that others treated him as equal in status to Yitzchak, and equally qualified to inherit.²⁹  In contrast to the above sources, though, Abarbanel does not present Yishmael himself as making any such claims.

Disinheritance

• Legal right – According to this approach, Sarah had every right to claim Yitzchak as the sole heir,³⁰ since he was born to the full wife, while Yishmael was the son of a maidservant.³¹  Moreover, Hashem had told Avraham, "וְאֶת בְּרִיתִי אָקִים אֶת יִצְחָק אֲשֶׁר תֵּלֵד לְךָ שָׂרָה", marking Yitzchak as the chosen son.  Thus, Sarah was not punishing Yishmael in stating that he would not inherit, but rather clarifying, while she was still alive, who the true heir was.³²
• Measure for measure punishment – According to Seforno, Sarah might be reacting to Yishmael's deeds measure for measure.  Yishmael libeled Yitzchak in an attempt to inherit everything, so Sarah ensured that he himself did not inherit at all.

Banishment – It is not clear why the disinheritance needed to be accompanied by banishment:

• Necessary clarification – Most of these sources might suggest that this was simply the clearest way of ensuring that there be no contest after death.³³ 
• Freedom not expulsion – It is also possible that Avraham did not actually expel Hagar and Yishmael, but simply released them from servitude.  See R. SaadiaTafsir Bereshit 21:9Tafsir Bereshit 21:14Commentary Bereshit 21:9About R. Saadia Gaon who translates "וַיְשַׁלְּחֶהָ"' as "released her".³⁴  He does not explain if this was also Sarah's intention when saying "גָּרֵשׁ הָאָמָה הַזֹּאת וְאֶת בְּנָהּ",‎³⁵ or if Avraham freed the two on his own, thus abiding by Sarah's wish that they leave, but without the harshness of banishment.

Biblical parallels – The disinheritance and expulsion of Yishmael and Hagar can be viewed as parallel to Avraham's later sending away of the sons of his concubines in Bereshit 25.  There, too, the context relates to the inheritance of Yitzchak,³⁶ and it is possible that in both stories, Avraham is simply acting to confirm Yitzchak's status as sole heir.³⁷

Ancient Near Eastern parallels – Several Ancient Near Eastern laws might shed light on our story:

• The Code of Hammurabi states that if a father refers to the child of a maidservant as his own, that child has equal rights to the inheritance.  If not, the child does not inherit, but upon the death of his father, he and his mother are released from servitude.  It is possible that Sarah's actions are to be understood in light of these Ancient Near Eastern norms.  Sarah asked Avraham to clarify, through Yishmael's expulsion, that he did not view him as a son, and thus that he had no rights to inherit.³⁸
• According to the Laws of Lipit Ishtar, if a man has children from a maidservant and he grants them freedom, they thereby forego any rights to the inheritance. In light of this, one might suggest that Sarah was asking Avraham to free (not banish) Hagar to thereby ensure that Yitzchak alone inherited.³⁹ 

Why is Avraham "upset about his son"? According to this approach, Avraham was upset about banishing a beloved son. Since Yishmael's actions were not particularly wicked,⁴⁰ although Avraham might have understood Sarah's desire that Yitzchak inherit, he still felt sorrow over Yishmael's fate. Radak even suggests that he would have rebuked Sarah had it not been for his desire to uphold household peace (‎שלום בית).‎⁴¹

Why is also Hagar expelled?

• For Hagar's benefit – Radak asserts that Sarah only asked that Hagar be expelled since she knew that a mother would never want to be separated from her son.
• To ensure inheritance – According to Abarbanel, Hagar needed to be banished from the home so that she would not be viewed as having equal wife status to Sarah.  If she was considered a full wife, even if Yishmael was expelled,  he would still inherit.⁴²
• Punishment – Seforno, in contrast, maintains that Yishmael had only libeled Yitzchak upon the advice of his mother, and so she was even more culpable than he.

Why does Hashem side with Sarah? Radak and Abarbanel explain that Hashem wanted the chosen line to emerge from Avraham and Sarah, as He explains to Avraham, "כִּי בְיִצְחָק יִקָּרֵא לְךָ זָרַע". He thus agreed that expulsion was necessary to prevent any contesting of the inheritance. Ralbag, though, posits that Hashem orchestrated the event to make sure that Yishmael could not negatively influence Yitzchak and thereby diminish his perfection.

"לֶחֶם וְחֵמַת מַיִם" – were there sufficient provisions? Radak, Ralbag, and Seforno all assert that Avraham supplied Hagar and Yishamel with gold and silver in addition to the food and water.  It was only because they got lost in the desert that the water supply ran out.  Abarbanel, in contrast, maintains that, in obedience to the Divine command, Avraham did not give them any money, thinking that it would constitute part of an inheritance.⁴³

Why does Hashem save Yishmael? According to this position, Yishmael did nothing terrible enough to deserve death.⁴⁴

Prophecy to Hagar – Abarbanel claims that Hashem saw that Hagar had been ready to despair of her son, leave him, and maybe even remarry.  In such a case, Yishmael would return to his father or Avraham would seek to protect him.  Either way, Yitzchak's inheritance would once again be endangered.  To prevent this, Hashem granted prophecy to Hagar to reassure her and endear Yishmael to her.

Aftermath – Abarbanel points out that Yishmale and Yitzchak together bury vraham,

Jealousy or Perceived Insult

Sarah's attitude towards Yishmael stemmed either from personal jealousy or a mistaken impression that Yishmael had bad intentions.

Sources:

Jubilees17:6-18About Jubilees, Ibn EzraBereshit 21:9Bereshit 21:14About R. Avraham ibn Ezra, ChizkuniBereshit 21:9-14About R. Chizkiyah b. Manoach, R. Avraham SabaTzeror HaMor Bereshit 21:9,11About R. Avraham Saba (Tzeror HaMor)

"מְצַחֵק" – According to all these opinions the word "מְצַחֵק" has no negative connotations and the verse is simply saying that Yishmael was happily playing and/or laughing.

Disinheritance and banishment – According to Jubilees, Ibn Ezra, and Chizkuni, seeing Yishmael play and be the center of attention while Yitzchak was still too young to do the same made Sarah jealous.  According to the Tzeror HaMor, in contrast, Sarah was insulted as she mistakenly thought that Yishmael's laughter was aimed at her.⁴⁵  These feelings led to her request that Yishmael be expelled.

Why is Avraham "upset about his son"? As Yishmael had done no wrong according to these commentators, Avraham was understandably upset about disinheriting and banishing his son.

Why is also Hagar expelled? These commentators do not address the issue but might suggest that Sarah's jealousy extended to the rival wife.  Alternatively, Sarah recognized that it would be cruel to separate mother and son.

Why does Hashem side with Sarah? According to the Tzeror HaMor, Hashem did not agree that Yishmael's behavior at the party warranted expulsion and viewed Sarah's treatment of him and Hagar as sinful.⁴⁶  It is unclear, then, why Hashem would tell Avraham to heed Sarah's words.  According to the Tzeror HaMor, this might have been the first step in Sarah's punishment; expelling Yishmael paved the way for his descendants to become an enemy nation.⁴⁷

"לֶחֶם וְחֵמַת מַיִם" – were there sufficient provisions? The Tzeror HaMor asserts that Sarah's descendants were punished when Yishmael's progeny refused water to the Children of Israel.⁴⁸  Though he does not say so, R. Saba might view this as a measure for measure punishment for not providing Yishmael with enough water when sending him away.

Why does Hashem save Yishmael? According to the Tzeror HaMor this was a punishment for Sarah. He suggests that it would have been better had Yishmael died from the lack of water, since then he would not have had descendants who would later oppress the Israelites. Due to Sarah's actions, though, he was saved so that he could later punish the nation.

¹ R. D"Z Hoffmann speaks about how Yishmael's presence endangered the righteous character of Yitzchak and also how it presented a threat to his inheritance, but he appears to find the first issue of greater import.

² See R. Akiva, the anonymous opinion in Tosefta, Tanchuma, Targum Pseudo-Jonathan, and Rashi. As evidence that the root "צחק" can be understood in this manner, R. Akiva points to Shemot 32:6, where the nation is "מצחק" before the Golden Calf.

³ See R. Yishmael and Rashi. R. Levi in Bereshit Rabbah and Pirkei deRabbi Eliezer speak not just in general of spilling blood, but have Yishmael attempting to kill Yitzchak himself. Support for this meaning is brought from the deadly "משחק" set up between the soldiers of Yoav and Avner in Shemuel II 2:14.

⁴ See R. Eliezer the son of R. Yose HaGelili who points to the story of Mrs. Potiphar in Bereshit 39:17, where the root "צחק" suggests sexual behavior.

⁵ R. Shimon B. Yochai questions whether it is realistic that a son brought up in Avraham's household would engage in such actions.  After all Hashem says of Avraham, "כִּי יְדַעְתִּיו לְמַעַן אֲשֶׁר יְצַוֶּה אֶת בָּנָיו וְאֶת בֵּיתוֹ אַחֲרָיו וְשָׁמְרוּ דֶּרֶךְ ה' לַעֲשׂוֹת צְדָקָה וּמִשְׁפָּט".

⁶ Ibn Kaspi also raises the possibility that Yishmael was gambling (‏"מְצַחֵק" = משחק בקוביא)‎.

⁷ All three understand the word "מְצַחֵק" somewhat literally to refer to scornful laughter.

⁸ Most of the sources would probably suggest that though the Torah does not say so explicitly, Sarah shared with Avraham that it was Yishmael's behavior which motivated her to expel him.  It is possible that the Torah only omits her words because it assumes that the reader is aware of her motivation from the preceding verse.

⁹ See Tosefta Sota, Shemot Rabbah, R. Avraham b. HaRambam, Ibn Kaspi and R. D"Z Hoffmann.

¹⁰ Cf. R. Saadia below who asserts that Sarah had permission to banish her son, but not to keep him from getting a monetary inheritance.

¹¹ See Midrash TannaimDevarim 14About Midrash Tannaim which already brings both approaches.

¹² See also the first opinion brought by Rashi.

¹³ This is supported by Hashem's response which uses the same language of "אַל יֵרַע בְּעֵינֶיךָ עַל הַנַּעַר וְעַל אֲמָתֶךָ " but includes Hagar as well as Yishmael. Furthermore, Hashem reassures Avraham that Yishmael will be a great nation,  addressing Avraham's concerns over his son's welfare rather than his behavior.

¹⁴ While the midrashic sources, Targum Pseudo-Jonathan and Rashi posit that Yishmael committed cardinal sins, Ramban maintains that he simply mocked Sarah.  As such, the varying interpretations of this verse are consistent with the exegetes' overall approaches.

¹⁵ Sarah had not wanted to hurt him by revealing it.

¹⁶ R. Avraham b. HaRambam, Ramban and Ibn Kaspi all portray Yishmael as much less wicked, and thus not so obviously deserving of expulsion.

¹⁷ According to Pirkei DeRabbi Eliezer, a mere flask of water would have sufficed due to Avraham's merits.

¹⁸ They renders the phrase "וַתֵּתַע בְּמִדְבַּר" metaphorically to mean that Hagar wandered after idolatry.

¹⁹ Targum Pseudo-Jonathan relates how both Hagar and Yishmael worshiped idols on their trek in the wilderness.  It appears from the Targum that, as a punishment for this action, Yishmael came down with a fever which depleted their water supply.  Pirkei DeRabbi Eliezer, in contrast, presents only Hagar as worshiping idolatry (and this is what causes their water to run out), while Yishmael himself prays to Hashem, the God of his father Avraham (again in contrast to Targum Pseudo Jonathan which has Hagar praying to the idolatrous god of her father). Numerous scholars have noted that this likely reflects Pirkei DeRabbi Eliezer's identification of Yishmael as the father of Islam, which he viewed as a monotheistic religion.

²⁰ He points out that had Sarah told Avraham to jump into a fiery furnace, obviously he would not be obligated to do so.  The Divine directive referred only to Sarah's request of banishment; when Hashem said "כֹּל אֲשֶׁר תֹּאמַר אֵלֶיךָ שָׂרָה שְׁמַע בְּקֹלָהּ" He had not meant to listen to literally "all" her requests.

²¹ Rashi is somewhat inconsistent in his understanding as he points to the Midrash which claims that Hashem saved Yishmael on his own merits, for his present righteous state ("בַּאֲשֶׁר הוּא שָׁם"). Yet, according to Rashi, Yishmael's present spiritual state was one of wickedness.

²² It tells of Avraham visiting his son and checking on his wives.  When he finds one wife not up to par, he lets Yishmael know and Yishmael acts on his advice to choose a new one.

²³ See also Targum Pseudo-Jonathan, Bereshit Rabbah, Tanchuma, and Rashi.  They all associate Keturah with Hagar.  For a full discussion of the identification and marriage, see Avraham's Many Wives.

²⁴ R. Saadia is not explicit and simply says that Yishmael was laughing and saying that Yitzchak would die before him. This might suggest that Yishmael was laughing because he believed that Yitzchak would never live to inherit.

²⁵ R. Shimon b. Yochai presents Yishmael as confident in his status as first-born.  In the version in the Sifre Devarim, he depicts Yishmael as not just laughing, but rather actively arguing with Yitzchak over the inheritance. Ramban questions this variation, arguing that it does not fit with the chronology of the verses, since the chapter assumes a very young Yitzchak. A toddler would not be arguing with his older brother over such matters. See, though, both Abarbanel and Shadal who raise the possibility that the mockery/fighting was not on the day of the party itself but at some point afterwards when Yitzchak was a little older.

²⁶ Radak portrays Yishmael as mocking Yitzchak, a child of elderly parents.  Sarah understood this mockery to stem from the fact that Yishmael viewed himself as on equal footing with Yitzchak, thinking that he had the same rights to inherit.  It is not clear from Radak, though, if this is really what motivated Yishmael's actions.

²⁷ Shadal presents Yiדhmael as mocking all the pomp and ceremony surrounding Yitzchak, thinking that Avraham and Sarah would die before he grew up, leaving Yishmael to inherit all. Cf. R. SaadiaTafsir Bereshit 21:9Tafsir Bereshit 21:14Commentary Bereshit 21:9About R. Saadia Gaon who has Yishmael taunt that Yitzchak would never survive to adulthood.

²⁸ According to this approach, Sarah's words "כׇּל הַשֹּׁמֵעַ יִצְחַק לִי" are understandable.

²⁹ Abarbanel contends that even before the incident Sarah feared that Yishmael would claim rights to the inheritance. Seeing him being the center of attention simply confirmed her suspicions that the longer he stayed, the more difficult disinheriting him would become.

³⁰ Cf. R. SaadiaTafsir Bereshit 21:9Tafsir Bereshit 21:14Commentary Bereshit 21:9About R. Saadia Gaon who claims, in contrast, that Sarah had no authority to disinherit Yishmael, only to distance him from home. He, thus, reinterprets "לֹא יִירַשׁ" to mean "will not dwell", pointing to Yeshayahu 34:11, "וִירֵשׁוּהָ קָאַת וְקִפּוֹד וְיַנְשׁוֹף וְעֹרֵב יִשְׁכְּנוּ בָהּ", where the word is parallel to "יִשְׁכְּנוּ".  See R. Avraham b. HaRambam above who also equates the disinheritance and banishment.

³¹ Avraham and Sarah's decision stands in contrast to that of Yaakov, who decided not to differentiate between the sons of his concubines and those of his real wives.

³²

³³ See, for instance, Abarbanel who claims that the longer Yishmael remained in the house, being treated as a full son, the harder it would be to clarify that he had no rights to the inheritance.  See also below that, according to the norms of the Ancient Near East (as stated in the Code of Hammurabi 170-171), if a father treated a maidservant's child as his own, that child could inherit after his death, but if he did not treat them as such, they could not.  If so, Sarah might have been asking Avraham to do a deed which made it explicit that he did not view Yishmael as a son, thereby clarifying to all that he had no rights to inherit.

³⁴ The piel form of "שלח"  means to release or free.  See this usage in the context of freeing slaves in Devarim 15.

³⁵ See E. Samet, who suggests that this was indeed Sarah's intent. He points to the Code of Hammurabi 171 which stipulates that if the child of a maidservant is not to inherit, the freedom of the maidservant and her children is assured upon the master's death. He suggests that Sarah and Avraham were following the norms of their time and that as soon as Sarah decided that Yishmael was not to inherit, she released Hagar from slave status.  As evidence that the  root, "גרש" can also mean "free" he points to Shemot 6:1 where the word is parallel to the root "שלח" and both refer to Paroh's freeing of the Nation of Israel. 
See also, below, that according to the Laws of Lipit Ishtar, a maidservant and child who are granted freedom do not have any rights to the inheritance.

³⁶ The text contrasts Yitzchak's inheriting all with Avraham's giving of gifts to the sons of the concubines and sending them away from Yitzchak while he was still alive.

³⁷ Abarbanel reads the action differently, though he also connects it to Chapter 21. He suggests that Avraham married the concubines only so that he could bear more children, and then send them away, so as to show Yishmael that it was nothing personal that led to his banishment. Hashem ordained that Yitzchak alone inherit. He hoped that his would alleviate Yishmael's anger and prevent fighting between him and Yitzchak, whom he would otherwise naturally despise. According to Abarbanel, Avraham was successful as proven by the fact that Yitzchak and Yishmael together bury Avraham.

³⁸ See, for example, Y. Roth-Rothem's סיפור גירוש ישמעאל, and "האכספוזיציה בסיפור גירוש ישמעאל" in Beit Mikra 43 (1998):113-124), and more recently, R"E. Samet, who similarly defend Sarah. 
See, though, Y. Fleishman, "גרש את האמה הזאת ואת בנה: מדוע צווה אברהם לשמע בקול שרה", Beit Mikra 44 (1999):142-162, who questions this reading of the law and its application.  He points out that the text implies that Yishmael had already been viewed by Avraham as a son, and that once son status is granted it is not so easily removed.

³⁹ See N. Sarna, Understanding Genesis, (New York,1966):155-157 who develops this idea.  Y. Fleishman in the article cited above, question this application of the law, asserting that the Code refers only to a maidservant and her son, while Hagar had concubine status and Yishmael was considered a full son.

⁴⁰ See Radak who asserts that Avraham loved Yishmael both because he was his firstborn and because "בדרך טובה היה הולך, כי הוא גדל עמו ולמדהו דרך ה'‏". 

⁴¹ See Radak Bereshit 16:6 where he similarly says that Sarah sinned in her treatment of Hagar and that Avraham did not rebuke her for the sake of peace.

⁴² According to Abrbanel, until the birth of Yitzchak, Sarah had assumed that Yishmael would inherit.  As such, she allowed Hagar to stay in the house as if she were a full wife, and did not mind it everyone treated  Yishamel as a full son. However, after Yitzchak was born, she realized that she had to do something to change the status quo and everyone's perceptions of who was the rightful heir.

⁴³ He, too, maintains that Avraham had really provided ample water and it only ran out after they got lost.

⁴⁴ Ralbag, nonetheless, asserts that Hashem listened to him only because of Avraham.

⁴⁵ He suggests that the elderly in general are very sensitive to people's laughter, assuming that they might be the subject. Thus, too, Sarah, in her old age, concluded that Yishmael was making fun of her.

⁴⁶ See his similar evaluation of Sarah's oppressive behavior towards Hagar in Chapter 16.

⁴⁷ Sarah was given freedom to sin, but also to suffer the consequences of her actions.

⁴⁸ See Yeshayahu 21:13-18 and the Tanchuma's understanding of these verses.