Abu Abd al-Rahman said: I was with Sayyiduna Abd al-Rahman bin Awf (may Allah be pleased with him) when Bilal (may Allah be pleased with him) passed by, and the people asked him about the ablution of the Messenger of Allah (peace and blessings be upon him). He said: "He (peace and blessings be upon him) would relieve himself, then come and perform ablution, and wipe over the turban and the leather socks."
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1096