It is narrated from Sayyiduna al-Mughirah bin Shu'bah (may Allah be pleased with him): I saw the Messenger of Allah (peace and blessings be upon him); he (peace and blessings be upon him) urinated, then came and performed ablution and wiped over his khuffs (leather socks). He placed his right hand on the right khuff and his left hand on the left khuff, then wiped over the upper part of both with a single wipe, and it is as if I am looking at the fingers of the Messenger of Allah (peace and blessings be upon him) on the khuffs.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1385