Sahih Muslim 1738
صحيح مسلم#1738SahihA'isha reported that the Messenger of Allah (ﷺ) used to observe Witr every night, and he would (at times) complete his Witr at the end of the night
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 6:167