Musnad Ahmad 28:78

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, ‘Ata’ ibn al-Sa’ib narrated to us, from his father, from ‘Abdullah ibn ‘Amr: From the Prophet, peace and blessings of Allah be upon him, that he commanded Fatimah and ‘Ali, when they took to their beds, to perform *tasbih* (saying *SubhanAllah*), *tahmid* (saying *Alhamdulillah*), and *takbir* (saying *Allahu Akbar*). ‘Ata’ did not know which of them was thirty-four to complete the hundred. He said: So ‘Ali said: "I have not abandoned them since." He said: Ibn al-Kawwa’ said to him: "Not even on the night of Siffin?" ‘Ali said: "Not even on the night of Siffin."