Salim bin Abdullah narrates from his father (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) used to pray on his riding animal in whichever direction it faced, and would also pray witr on the riding animal, except for the obligatory prayer. In the hadith of Abu Dawud the word 'qibala' (towards) does not occur.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4594