It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) used to offer voluntary prayer on the back of his mount. He (peace and blessings be upon him) paid no attention to whichever way his face was turned, and he (peace and blessings be upon him) would make gestures with his head.
And Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) also used to do the same.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2209
It is narrated from Sayyiduna Jabir bin Abdullah al-Ansari (may Allah be pleased with him) that he said: I saw the Prophet (peace and blessings be upon him) offering voluntary prayers on his mount facing every direction, but he (peace and blessings be upon him) would bend lower in prostration than in bowing. He would offer the prayer (on the mount) by gestures.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2210
It is narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) that he said: the Messenger of Allah (peace and blessings be upon him) sent me on some errand. When I returned, he was praying on his mount facing the east, and he would bend lower in prostration than in bowing. I greeted him (peace and blessings be upon him) with salam, but he (peace and blessings be upon him) did not return my greeting. When he (peace and blessings be upon him) had finished the prayer, he (peace and blessings be upon him) said: "I was praying."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2211