Musnad Abu Ya'la al-Mawsili 154:140

Abu al-Rabi' narrated to us, Hammad narrated to us, Ayyub and Budayl narrated to us, from Abdullah ibn Shaqiq, from Ibn Umar: That a man asked the Prophet, peace and blessings of Allah be upon him, "How is the night prayer?" He said, "Two by two. If you fear the morning, then pray one rak'ah, and make the end of your prayer witr." Then he asked him at the turn of the year, and I was in that same place from the Messenger of Allah, but I do not know if it was that same man or another man, and he said to him the same thing.