Musannaf Ibn Abi Shayba 3:4360

Waki’ narrated to us, he said: Hammad bin Salamah narrated to us, from Bishr bin Harb Abu ‘Amr, he said: I heard Rafi’ bin Khadij say: As for me, I perform Witr, then when I stand [for the night prayer], I pray two by two, and I leave my Witr [as it was].