Musannaf Ibn Abi Shayba 3:3319

Hushaym narrated to us, from Ibn ‘Awn, from Makhul, who said: Someone who witnessed Sa‘id ibn al-‘As informed me that he sent for four men from among the Companions of the Tree (al-Shajara) and asked them about the *takbir* (saying "Allahu Akbar") in the *‘Eid* prayer. They said: "Eight *takbirs*." He (Makhul) said: I mentioned that to Ibn Sirin, and he said: "They spoke the truth, but he (Sa‘id) neglected the *takbir* of the opening of the prayer."