Musnad Ahmad 788:248

Zayd ibn al-Hubab narrated to us, he said: Ibn Thawban narrated to us, from his father, from Makhul, he said: Abu A’isha narrated to me—and he was a companion of Abu Hurayrah—that Sa’id ibn al-’As invited Abu Musa al-Ash’ari and Hudhayfah ibn al-Yaman, may Allah be pleased with them, and said: "How did the Messenger of Allah, peace and blessings of Allah be upon him, perform the takbir during al-Fitr and al-Adha?" Abu Musa said: "He used to perform four takbirs, like his takbir over the funeral prayers." Hudhayfah confirmed this for him. Abu A’isha said: "I have not forgotten, after his statement, 'like his takbir over the funeral prayers,'" and Abu A’isha was present with Sa’id ibn al-’As.