The Book of Prayer - Travellers
6/4. Chapter:
It is permissible to offer voluntary prayers atop one’s mount when travelling, no matter what direction it is facing
Sahih Muslim
وَحَدَّثَنِي عِيسَى بْنُ حَمَّادٍ الْمِصْرِيُّ، أَخْبَرَنَا اللَّيْثُ، حَدَّثَنِي ابْنُ الْهَادِ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّهُ قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُوتِرُ عَلَى رَاحِلَتِهِ .
'Abdullah b. 'Umar reported that the Messenger of Allah (ﷺ) used to observe Witr prayer on his ride.
Reference : Sahih Muslim 700hIn-book reference : Book 6, Hadith 48USC-MSA web (English) reference : Book 4, Hadith 1504