Musnad Abu Ya'la al-Mawsili 106:28

Ahmad narrated to us, Abu Dawud narrated to us, Shu'bah narrated to us, from al-Hakam, who said: I heard Ibn Abi Layla narrating from al-Bara', who said: The prayer of the Messenger of Allah, may Allah bless him and grant him peace, when he bowed, and when he raised his head from bowing, and when he prostrated, and when he raised his head from the two prostrations, was nearly equal.