(45) باب الْوِتْرِ بِثَلاَثَ عَشْرَةَ رَكْعَةً
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." (ID)
Reference (ID): Sunan an-Nasa'i 1727 (ID)
In-book reference (ID): Book 20, Hadith 130 (ID)
English translation (ID): Vol. 2, Book 20, Hadith 1728 (ID)