Sayyiduna Abdullah bin Umar (may Allah be pleased with them) narrates that the Messenger of Allah (peace and blessings be upon him) used to perform all voluntary prayers, including Witr, on his mount, facing whichever direction it was headed; however, he did not perform obligatory prayers on his mount.
Hadith Referenceالمنتقى ابن الجارود / كتاب الصلاة / 270
Hadith Gradingغلام مصطفےٰ ظهير امن پوري:صحيح
Hadith Takhrijاز غلام مصطفےٰ ظهير امن پوري:«صحيح البخاري : 1098 ، صحيح مسلم : 700/39»