The Book of Qiyam Al-Lail (The Night Prayer) and Voluntary Prayers During the Day
20/45. Chapter:
Witr with thirteen rak'ahs
Sunan an-Nasai
أَخْبَرَنَا أَحْمَدُ بْنُ حَرْبٍ، قَالَ حَدَّثَنَا أَبُو مُعَاوِيَةَ، عَنِ الأَعْمَشِ، عَنْ عَمْرِو بْنِ مُرَّةَ، عَنْ يَحْيَى بْنِ الْجَزَّارِ، عَنْ أُمِّ سَلَمَةَ، قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُوتِرُ بِثَلاَثَ عَشْرَةَ رَكْعَةً فَلَمَّا كَبِرَ وَضَعُفَ أَوْتَرَ بِتِسْعٍ .
It was narrated that Umm Salamah said: "The Messenger of Allah (ﷺ) used to pray witr with thirteen rak'ahs, but when he grew older and weaker he prayed witr with nine."
Reference : Sunan an-Nasa'i 1727In-book reference : Book 20, Hadith 130English translation : Vol. 2, Book 20, Hadith 1728