Sahih Muslim 1764
صحيح مسلم#1764SahihAbu Sa'id (al Khudri) reported Allah's Apostle (ﷺ) as saying:Observe Witr prayer before it is morning. Abu Sa'id reported that they (the Prophet's Companions) asked the Messenger of Allah (ﷺ) about Witr (prayer). (In reply to their inquiry) he said: Observe Witr prayer before it is morning
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: 6:193