حَدَّثَنَا قُرَّانُ بْنُ تَمَّامٍ عَنْ عُبَيْدِ اللَّهِ عَنِ نَافِعٍ عَنِ ابْنِ عُمَرَ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَانَ يُصَلِّي عَلَى رَاحِلَتِهِ حَيْثُ تَوَجَّهَتْ بِهِ
مسند امام احمد بن حنبل · Hadith 4956
It was narrated from Ibn 'Umar that the Messenger of Allah (PBUH) used to pray (naafil) atop his mount no matter what direction it was facing.
Translated by Dr. Muhammad Muhsin Khan · Reviewed by Islamic University of Madinah · Published March 2020