(17) باب صَلاَةِ اللَّيْلِ وَعَدَدِ رَكَعَاتِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي اللَّيْلِ وَأَنَّ الْوِتْرَ رَكْعَةٌ وَأَنَّ الرَّكْعَةَ صَلاَةٌ صَحِيحَةٌ
'A'isha thus reported about the (night prayer) of the Messenger of Allah (ﷺ):
He used to sleep in the early part of the night, and woke up in the latter part. If he then wished intercourse with his wife, he satisfied his desire, and then went to sleep; and when the first call to prayer was made he jumped up (by Allah, she, i. e. 'A'isha, did not say" he stood up" ), and poured water over him (by Allah she, i. e. 'A'isha, did not say that he took a bath but I know what she meant) and if he did not have an intercourse, he performed ablution, just as a man performs ablution for prayer and then observed two rak'ahs.
Reference: Sahih Muslim 739
In-book reference: Book 6, Hadith 157
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1612