Sahih Muslim 1756
صحيح مسلم#1756SahihNafi' reported Ibn 'Umar as saying:He who observed the night prayer should make Witr the end of his prayer before dawn. The Messenger of Allah (ﷺ) used to order them thus
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: 6:185