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
وَحَدَّثَنَا ابْنُ الْمُثَنَّى، وَابْنُ، بَشَّارٍ قَالاَ حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، حَدَّثَنَا شُعْبَةُ، عَنْ أَنَسِ بْنِ سِيرِينَ، قَالَ سَأَلْتُ ابْنَ عُمَرَ . بِمِثْلِهِ وَزَادَ وَيُوتِرُ بِرَكْعَةٍ مِنْ آخِرِ اللَّيْلِ . وَفِيهِ فَقَالَ بَهْ بَهْ إِنَّكَ لَضَخْمٌ .
Anas b. Sirin reported: I asked Ibn 'Umar like this (as recorded in the previous hadith) and he made this addition:" And he (the Holy Prophet) made the end of the night prayer as odd number by one rak'ah." And there is also (this addition):" Stop, stop, you are bulky."
Reference : Sahih Muslim 749hIn-book reference : Book 6, Hadith 191USC-MSA web (English) reference : Book 4, Hadith 1646