It is narrated from Ibn Umar (may Allah be pleased with them) that on the day of Eid al-Fitr, he would go towards the Eid ground in the morning when the sun had risen. He would recite the takbeerat in the Eid ground until the imam sat down, at which point he would stop reciting the takbeerat.
Hadith Referenceمسند الإمام الشافعي / كتاب العيدين والأضاحي والاستسقاء / 477
Hadith Takhrijاسناده ضعیف : لضعف شیخ الشافعى اخرجه البيهقي في المعرفة السنن والآثار (1870)۔