The Book of Prayer - Travellers
6/20. Chapter:
The night prayers are two by two, and Witr is one rakah at the end of the night
Sahih Muslim
وَحَدَّثَنِي زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا عَبْدُ الصَّمَدِ، حَدَّثَنَا هَمَّامٌ، حَدَّثَنَا قَتَادَةُ، عَنْ أَبِي مِجْلَزٍ، قَالَ سَأَلْتُ ابْنَ عَبَّاسٍ عَنِ الْوِتْرِ، فَقَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " رَكْعَةٌ مِنْ آخِرِ اللَّيْلِ " . وَسَأَلْتُ ابْنَ عُمَرَ فَقَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " رَكْعَةٌ مِنْ آخِرِ اللَّيْلِ " .
Abu Mijlaz reported: I asked Ibn 'Abbas about the Witr prayer. He said: I heard the Messenger of Allah (ﷺ) as saying: It is a rak'ah at the end of the night prayer.
Reference : Sahih Muslim 753In-book reference : Book 6, Hadith 188USC-MSA web (English) reference : Book 4, Hadith 1643