(17) باب صَلاَةِ اللَّيْلِ وَعَدَدِ رَكَعَاتِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي اللَّيْلِ وَأَنَّ الْوِتْرَ رَكْعَةٌ وَأَنَّ الرَّكْعَةَ صَلاَةٌ صَحِيحَةٌ
'A'isha reported:
The Messenger of Allah (ﷺ) used to observe thirteen rak'ahs of the night prayer. Five out of them consisted of Witr, and he did not sit, but at the end (for salutation).
Reference: Sahih Muslim 737 a
In-book reference: Book 6, Hadith 149
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1604