Amr bin Shu'ayb narrates from his father, and he from his grandfather (may Allah be pleased with him), that the Messenger of Allah (peace and blessings be upon him) would say seven and five takbirs on the day of Eid al-Fitr and Eid al-Adha, that is, seven in the first rak'ah and five in the second rak'ah, besides the opening takbir (takbir al-tahrimah).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة العيدين / 6171