(17) باب صَلاَةِ اللَّيْلِ وَعَدَدِ رَكَعَاتِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي اللَّيْلِ وَأَنَّ الْوِتْرَ رَكْعَةٌ وَأَنَّ الرَّكْعَةَ صَلاَةٌ صَحِيحَةٌ
Abu Salama is reported to have said. I came to 'A'isha. I said:
O mother, inform me about the prayer of the Messenger of Allah (ﷺ). She said: His (night prayer) in Ramadan and (during other months) was thirteen rak'ahs at night including two rak'ahs of fajr.
Reference: Sahih Muslim 738 d
In-book reference: Book 6, Hadith 155
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1610