Musnad Abu Ya'la al-Mawsili 3:318

Abu Khaythama narrated to us, Ibn 'Uyaynah narrated to us, from 'Ubayd Allah ibn Abi Yazid, from Mujahid, from Ibn Abi Layla, from 'Ali, who said: Fatimah came to the Prophet, may Allah bless him and grant him peace, asking him for a servant. He said: "Shall I guide you or teach you what is better for you than that? When you go to your bed, glorify Allah (say *SubhanAllah*) thirty-three times, and magnify Him (say *Allahu Akbar*) and praise Him (say *Alhamdulillah*)—one of them thirty-three times and the other thirty-four times." 'Ali said: "I have not abandoned it since I heard it." It was said to him: "Not even on the night of Siffin?" He said: "Not even on the night of Siffin."