Musannaf Ibn Abi Shayba 3:3252

Yazid ibn Harun narrated to us, from Ibn Abi Dhi'b, from al-Zuhri, who said: The people used to say the takbir on the day of Eid when they left their houses until they reached the prayer ground, and until the Imam came out. When the Imam came out, they would fall silent. Then, when he said the takbir, they would say the takbir.