Kathir bin Abdullah 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 takbirs in the first rak'ah of the two Eids, and five takbirs in the second rak'ah, before the recitation."
Abu Isa said: I asked Muhammad, meaning al-Bukhari, about this hadith, and he said: There is nothing in this chapter more authentic than this, and I hold by it. He said: And the hadith of Abdullah bin Abd al-Rahman al-Ta'ifi from Amr bin Shu'ayb, from his father, from his grandfather, in this chapter is also sahih (authentic).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة العيدين / 6173