Musannaf Ibn Abi Shayba 3:4770

Waki' narrated to us, from Hammad ibn Salamah, from Muhammad ibn Ziyad, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Does the one who raises his head before the Imam not fear that Allah will turn his head into the head of a donkey?"