Sunan an-Nasa'i 1328
سنن النسائي#1328SahihIt was narrated from 'Urwah (that) Aishah said:"The Messenger of Allah (ﷺ) used to pray eleven rak'ahs, making it odd (witr) by one between the time when he finished 'Isha and dawn, and he would prostrate for as long as it takes one of you to recite fifty verses before raising his head
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: 13:150