Sayyiduna Ibn Umar (may Allah be pleased with them both) said: "I saw the Messenger of Allah (peace and blessings be upon him) praying on his donkey while his donkey was facing towards Khaybar; he ((peace and blessings be upon him)) was praying by gestures (for bowing and prostration)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13218