Musannaf Ibn Abi Shayba 3:3328

Hushaym narrated to us, from Ash'ath, from Kardus, from Ibn Abbas, who said: When it was the night of the Eid, Al-Walid ibn Uqbah sent to Ibn Mas'ud, Abu Mas'ud, Hudhayfah, and Al-Ash'ari. He said to them: "The Eid is tomorrow, so how is the Takbir?" Abdullah said: "He stands and says four Takbirs, and he recites the Opening of the Book (Al-Fatiha) and a Surah from the Mufassal—not from its long ones nor from its short ones—then he bows. Then he stands and recites. When he finishes the recitation, he says four Takbirs, then he bows on the fourth."