Musnad Abu Ya'la al-Mawsili 131:14

Abu Khaythama narrated to us, Jarir narrated to us, from al-Mukhtar ibn Fulful, from Anas ibn Malik, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "I am your Imam, so do not precede me in bowing nor in prostration, for indeed I see you from in front of me and from behind me."