Sayyiduna Abd al-Rahman bin Awf (may Allah be pleased with him) asked Sayyiduna Bilal (may Allah be pleased with him) about the ablution of the Prophet (peace and blessings be upon him), and he said: When he (peace and blessings be upon him) had relieved himself, I would bring water; he (peace and blessings be upon him) would perform ablution and wipe over his turban and his khuffs (leather socks).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1367
It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) "used to wipe over the khuffs (leather socks) and the head cover (turban)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1368