Musnad Ahmad 790:180

Hassan ibn Musa and Sulayman ibn Harb narrated to us, they said: Hammad ibn Zayd narrated to us, Ghaylan ibn Jarir narrated to us, from Mutarrif, who said: I prayed a prayer behind Ali ibn Abi Talib, I and Imran ibn Husayn. When he prostrated, he said "Allahu Akbar" (God is the Greatest), and when he raised his head, he said "Allahu Akbar," and when he rose from the two rak'ahs, he said "Allahu Akbar." When he finished the prayer, Imran took my hand and said: "This has reminded me of the prayer of Muhammad, may God bless him and grant him peace," or he said: "He has prayed for us the prayer of Muhammad, may God bless him and grant him peace."