Sunan an-Nasa'i 1722
سنن النسائي#1722SahihIt was narrated that Aishah said:"The Messenger of Allah (ﷺ) used to pray witr with nine rak'ahs, then he would pray two rak'ahs sitting down. When he grew weaker he prayed witr with seven rak'ahs, then he prayed two rak'ahs sitting down
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih
In-book reference: 20:125