Musannaf Ibn Abi Shaybah

Muhammad says that the night prayer is in sets of two rak‘ahs, and at the end of the night there is one rak‘ah of witr. And (Imam) Abu Hanifa’s statement is mentioned that: If you wish, then pray two rak‘ahs, and if you wish, then pray four rak‘ahs, and if you wish, then pray six rak‘ahs, and do not separate them.