Sahih Muslim 749 g
The Book of Prayer - Travellers
The night prayers are two by two, and Witr is one rakah at the end of the night
Anas b. Sirin reported: I asked Ibn 'Umar to tell me about the practice of the Prophet (ﷺ) in regard to two rak'ahs before the dawn prayer: Should I make lengthy recitation in them? He said: The Messenger of Allah (ﷺ) used to observe, the night prayer in pairs and then made the number odd by observing one rak'ah. I said: I am not asking you about it. He said: You are a bulky man, will you not show me the patience to narrate to you the hadith completely? The Messenger of Allah (ﷺ) used to observe the night prayer in pairs and then made the number odd by observing one rak'ah, and then he observed two rak'ahs before dawn quite close to the call for prayer (Khalaf said:" Did you see [yourself the Prophet (ﷺ) observing] the two rak'ahs before the dawn?" and he made no mention of prayer.)