Sahih Muslim Book 6, Hadith 47
'Abdullah b. Dinar reported on the authority of Ibn 'Umar that the Messenger of Allah (ﷺ) used to observe prayer on his ride (no matter) in which direction it had its face turned. 'Abdullah b. Dinar said that Ibn 'Umar used to do like that.
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.
'Abdullah b. 'Umar reported that the Messenger of Allah (ﷺ) used to observe Witr prayer on his ride.