(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 pray in the night and when he observed Witr, he said to me: O 'A'isha, get up and observe Witr.
Reference: Sahih Muslim 744 a
In-book reference: Book 6, Hadith 163
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1618