Sahih Muslim 1610
صحيح مسلم#1610SahihIbn 'Umar reported that the Messenger of Allah (ﷺ) used to say Nafl prayer on (the back of) his camel in whatever direction it took him
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: 6:41