Shirat HaYam
Overview
Saying Shirat HaYam seems to be a minhag Eretz Yisraeli. It was then adopted, in the Geonim time, in Bavel although not everyone agreed on saying it. Some said it all the time, some said it only on Shabbat and some didn't say it at all.During the Rishonim time, in Ashkenaz and France they said Shirat HaYam as part of Pesukei DeZimra although in Spain and Provence they said it after Yishtabach as not part of Pesukei DeZimra. Only later did everyone start saying Shirat HaYam before Yishtabach as part of Pesukei DeZimra.