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
حَدَّثَنَا شَيْبَانُ بْنُ فَرُّوخَ، حَدَّثَنَا عَبْدُ الْوَارِثِ، عَنْ أَبِي التَّيَّاحِ، قَالَ حَدَّثَنِي أَبُو مِجْلَزٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الْوِتْرُ رَكْعَةٌ مِنْ آخِرِ اللَّيْلِ " .
Ibn 'Umar reported Allah's Messenger (ﷺ) as saying: Witr is a rak'ah at the end of the prayer.
Reference : Sahih Muslim 752aIn-book reference : Book 6, Hadith 186USC-MSA web (English) reference : Book 4, Hadith 1641