It is narrated from Hazrat Abu Saeed (may Allah be pleased with him) and Ibn Umar (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) used to offer voluntary prayers on his mount, regardless of which direction it was facing, and he would perform this prayer by gestures, bowing lower in prostration than in bowing.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 11701
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذان إسنادان ضعيفان لضعف ابن أبى ليلي و عطية العوفي