Musnad Ahmad 27:1021

'Ali ibn 'Asim narrated to us, Khalid al-Hadhdha' informed us, from 'Abdullah ibn Shaqiq al-'Uqayli, from Ibn 'Umar, who said: A man from the people of the desert called out to the Messenger of Allah, may Allah bless him and grant him peace, and I was between him and the Bedouin. He said: "O Messenger of Allah, how is the prayer of the night?" He said: "Two by two. Then, if you fear the morning, [pray] one, and two rak'ahs before the dawn prayer."