(17) باب صَلاَةِ اللَّيْلِ وَعَدَدِ رَكَعَاتِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي اللَّيْلِ وَأَنَّ الْوِتْرَ رَكْعَةٌ وَأَنَّ الرَّكْعَةَ صَلاَةٌ صَحِيحَةٌ
'A'isha reported:
When the Messenger of Allah (ﷺ) had prayed the two rak'ahs (Sunan) of the dawn prayer, he would talk to me if I was awake, otherwise he would lie down.
Reference: Sahih Muslim 743 a
In-book reference: Book 6, Hadith 161
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1616