6. The Book of Prayer - Travellers - كتاب صلاة المسافرين وقصرها
20) Chapter: Night Prayer Consists Of Pairs Of Rak'ahs And Witr Is A Rak'ah At The End Of The Night
'Abdullah b. 'Umar reported:
A man stood up and said. Messenger of Allah, how is the night prayer? The Messenger of Allah (ﷺ) said: The night prayer consists of pair, but if you apprehend the rise of dawn, make it odd number by observing one rak'ah.