Musnad Ahmad 5:662

Yazid narrated to us, Al-Awwam informed us, from Amr ibn Murrah, from Abd al-Rahman ibn Abi Layla, from Ali, who said: "The Prophet, peace and blessings of Allah be upon him, came to us one night until he placed his foot between me and Fatimah. He taught us what we should say when we go to our beds: thirty-three glorifications (tasbih), thirty-three praises (tahmid), and thirty-four exaltations (takbir)." Ali said: "I have not abandoned it ever since." A man said to him: "Not even on the night of Siffin?" He said: "Not even on the night of Siffin."