Musannaf Ibn Abi Shayba 3:4370

Abu Bakr ibn Ayyash narrated to us, from al-A’mash, from Ibrahim, from Alqama, who said: If a man performs the Witr prayer at the beginning of the night, then it occurs to him to pray at the end of the night, let him pray two rak'ahs by two rak'ahs until he reaches the morning.