Musannaf Ibn Abi Shayba 35:355

Muhammad ibn Abi ‘Adi narrated to us, from Ibn ‘Awn, from Muhammad, who said: The night prayer is two by two. And the Witr is one rak’ah from the end of the night. And he mentioned that Abu Hanifah said: If you wish, you may pray two rak’ahs, and if you wish, four, and if you wish, six, not separating between them.