It is narrated from Sayyiduna Mughirah bin Shu'bah (may Allah be pleased with him); he said: I was with the Messenger of Allah (peace and blessings be upon him) on one of his (peace and blessings be upon him) journeys, and whenever the Messenger of Allah (peace and blessings be upon him) went to relieve himself, he would go far away. He (peace and blessings be upon him) said: "Follow me with water." So I followed him (peace and blessings be upon him) with water in a vessel. He (peace and blessings be upon him) was wearing a Syrian jubbah with tight sleeves, so he (peace and blessings be upon him) brought his hands out from under the jubbah, performed ablution, and wiped over his leather socks.
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 18188