Musnad Abu Ya'la al-Mawsili 131:19

Uthman ibn Abi Shaybah narrated to us, Jarir narrated to us, from al-Mukhtar ibn Fulful, from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I am your Imam, so do not precede me in bowing nor in prostration, for I see you from in front of me and from behind me."