Musnad Ahmad 524:3

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Yahya ibn Abi Kathir, from Abu Salamah ibn 'Abd al-Rahman, from 'Amr ibn Umayyah al-Damri, who said: "I saw the Messenger of Allah, peace and blessings of Allah be upon him, wiping over the khuffayn (leather socks)."