Ja'far bin Muhammad (may Allah have mercy on him) narrates that the Prophet (ﷺ), Abu Bakr, and Umar (may Allah be pleased with them) said seven and five takbeers in the Eid and Istisqa prayers, and performed the prayer before the sermon, and recited aloud in them.
Hadith Referenceمسند الإمام الشافعي / كتاب العيدين والأضاحي والاستسقاء / 485