The Book of Qiyam Al-Lail (The Night Prayer) and Voluntary Prayers During the Day
20/34. Chapter:
How many (rak'ahs) is witr?
Sunan an-Nasai
أَخْبَرَنَا الْحَسَنُ بْنُ مُحَمَّدٍ، عَنْ عَفَّانَ، قَالَ حَدَّثَنَا هَمَّامٌ، قَالَ حَدَّثَنَا قَتَادَةُ، عَنْ عَبْدِ اللَّهِ بْنِ شَقِيقٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَجُلاً، مِنْ أَهْلِ الْبَادِيَةِ سَأَلَ رَسُولَ اللَّهِ صلى الله عليه وسلم عَنْ صَلاَةِ اللَّيْلِ قَالَ " مَثْنَى مَثْنَى وَالْوَتْرُ رَكْعَةٌ مِنْ آخِرِ اللَّيْلِ " .
It was narrated from Ibn 'Umar that: A man from among the people of the desert asked the Messenger of Allah (ﷺ) about prayer at night. He said:"(It is) two by two, and Witr is one rak'ah at the end of the night."
Reference : Sunan an-Nasa'i 1691In-book reference : Book 20, Hadith 94English translation : Vol. 2, Book 20, Hadith 1692