"The messenger of Allah (peace be upon him) used to pray atop his mount while travelling, facing whatever direction it was facing." (One of the narrators) Malik said: "Abdullah bin Dinar said: and Ibn Umar used to do likewise".  

كَانَ رَسُولُ اللَّهِ ﷺ يُصَلِّي عَلَى رَاحِلَتِهِ فِي السَّفَرِ حَيْثُمَا تَوَجَّهَتْ بِهِ قَالَ مَالِكٌ قَالَ عَبْدُ اللَّهِ بْنُ دِينَارٍ وَكَانَ ابْنُ عُمَرَ يَفْعَلُ ذَلِكَ  

"The messenger of Allah (peace be upon him) used to pray atop his mount while traveling, facing whatever direction it was facing, and he would pray witr atop it, but he did not pray the prescribed prayers atop it ".  

كَانَ رَسُولُ اللَّهِ ﷺ يُصَلِّي عَلَى الرَّاحِلَةِ قِبَلَ أَىِّ وَجْهٍ تَوَجَّهُ بِهِ وَيُوتِرُ عَلَيْهَا غَيْرَ أَنَّهُ لاَ يُصَلِّي عَلَيْهَا الْمَكْتُوبَةَ