"The Messenger of Allah ﷺ used to pray on his mount while on a journey, no matter what direction it was facing." Malik said: "Abdullah bin Dinar said: 'And Ibn 'Umar used to do likewise.'" (Using translation from Nasāʾī 492)  

«كَانَ رَسُولُ اللهِ ﷺ يُصَلِّي عَلَى رَاحِلَتِهِ فِي السَّفَرِ حَيْثُ تَوَجَّهَتْ بِهِ» قَالَ مَالِكٌ قَالَ عَبْدُ اللهِ بْنُ دِينَارٍ وَكَانَ ابْنُ عُمَرَ يَفْعَلُ ذَلِكَ  

Salim b. 'Abdullah reported on the authority of his father that the Messenger of Allah (may peace be. upon him) used to observe Nafl (supererogatory) prayer on his ride no matter in what direction it turned its face, and he observed Witr too on it, but did not observe obligatory prayer on it. (Using translation from Muslim 700i)  

«كَانَ رَسُولُ اللهِ ﷺ يُسَبِّحُ عَلَى الرَّاحِلَةِ قِبَلَ أَيِّ وَجْهٍ تَوَجَّهُ وَيُوتِرُ عَلَيْهَا غَيْرَ أَنَّهُ لَا يُصَلِّي عَلَيْهَا الْمَكْتُوبَةَ»