Sahih Muslim Book 6, Hadith 41
Ibn '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.
A hadith like this that Ibn 'Abbas ordered his Mu'adhdhin (to summon people to prayer and then make announcement to say prayer in their houses) on Friday which was a rainy day, has been transmitted by 'Abdullah b. Harith. Wuhaib, however, says that he did not hear it from him.
Ibn 'Umar reported that the Apostle (ﷺ) used to pray on (the back of) his camel in whatever direction it took him.