Sahih Muslim 1615
صحيح مسلم#1615SahihSa'id b. Yasar reported:I was travelling along with Ibn 'Umar on the way to Mecca. Sa'id said: When I apprehended dawn, I dismounted (the ride) and observed Witr prayer and then again joined him. Ibn 'Umar said to me: Where were you? I said: I apprehended the appearance of dawn, so I dismounted and observed Witr prayer. Upon this 'Abdullah said: Is there not a model pattern for you in the Messenger of Allah (ﷺ)? I said: Yes, by Allah, and (then) he said: The Messenger of Allah (ﷺ) used to observe Witr prayer on the camel's back
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: 6:46