Abdullah bin Abi Musa (may Allah have mercy on him) reports from his father that when Sa'id bin al-As summoned Sayyiduna Abu Musa, Sayyiduna Hudhayfah and Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with them) at dawn, before praying the morning prayer, and asked them about the takbirs on the day of Eid, Sayyiduna Hudhayfah (may Allah be pleased with him) said: Ask al-Ash'ari (Sayyiduna Abu Musa). Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him) said: Ask Sayyiduna Abdullah (bin Mas'ud), for he is the most knowledgeable of us and the earliest of us (in Islam). So he asked him, and he said: "Begin with four takbirs and end with four takbirs: say one takbir, then add three more to it, then say the takbir and bow. Then when you rise from the prostration, recite, then say four takbirs, then bow."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9487