Musannaf Ibn Abi Shayba 3:3253

Yazid narrated to us, from Ibn Abi Dhi'b, from Shu'bah, who said: I was leading Ibn Abbas on the day of Eid. He heard the people saying the takbir (Allahu Akbar), so he said: "What is the matter with the people?" I said: "They are saying the takbir." He said: "Are they saying the takbir?" He said: "Is the Imam saying the takbir?" I said: "No." He said: "Are the people mad?"