It is narrated from Sayyiduna Mughirah bin Shu'bah (may Allah be pleased with him); he said: "The Messenger of Allah (peace and blessings be upon him) was on one of his military expeditions when he (peace and blessings be upon him) dismounted to relieve himself, so I brought him (peace and blessings be upon him) water for ablution. He (peace and blessings be upon him) was wearing a tight cloak (jubbah), so he (peace and blessings be upon him) brought his hand out from beneath it. I poured water for him (peace and blessings be upon him), and he (peace and blessings be upon him) performed ablution and wiped over his leather socks."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 18121