Musnad Abu Ya'la al-Mawsili 3:292

Abu Musa narrated to us, Yazid bin Harun narrated to us, al-Awam bin Hawshab informed us, Amr bin Murrah narrated to me, from Abd al-Rahman bin Abi Layla, from Ali, who said: The Messenger of Allah (may Allah bless him and grant him peace) came to us 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 since." A man said to him: "Not even on the night of Siffin?" He said: "Not even on the night of Siffin."