It is narrated from Sayyiduna Amr bin Awf bin Milhah al-Muzani (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) used to say seven takbirs in the first rak'ah of the two Eid (prayers), and five takbirs in the second rak'ah before the recitation.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14080