Sayyiduna Ibn Umar (may Allah be pleased with them both) narrates that the Messenger of Allah (peace and blessings be upon him) used to pray, and his mount would take him in whichever direction it turned his face. The wording of the narration from Abdullah bin Saeed is that the Prophet (peace and blessings be upon him) continued to pray on his mount, regardless of whichever direction his mount turned his face. Abu Kuraib and Abdullah bin Saeed say that Sayyiduna Ibn Umar (may Allah be pleased with them both) also used to pray in the same manner.