Hadith #1510 (Sahih Muslim)
Book: The Book of Prayer - Travellers
Narrator(s): Sa'id bin Yasar, Abu al-Hubab سعيد بن يسار أبو الحباب
Grade: Sahih

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.

Source: https://parallelquran.com/hadith/sahih-muslim-1510/