Sa'id bin al-As (may Allah be pleased with him) came before Eid al-Adha and sent a man to Abdullah bin Mas'ud, Abu Musa and Abu Mas'ud al-Ansari (may Allah be pleased with them) to ask them about the takbirs. They left the decision to Abdullah bin Mas'ud (may Allah be pleased with him).
Then Abdullah bin Mas'ud (may Allah be pleased with him) said: Say four takbirs, then recite, then bow with the fifth takbir; then stand and recite, then say four takbirs and bow with the fourth takbir.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة العيدين / 6184