Musnad Ahmad 2:47

'Affan narrated to us, Khalid narrated to us, from Yazid ibn Abi Ziyad, from 'Asim ibn 'Ubayd Allah, from his father, or from his grandfather. From 'Umar ibn al-Khattab, he said: I saw the Messenger of Allah, peace and blessings of Allah be upon him, after having had a minor impurity (hadath), perform ablution (wudu) and wipe over his leather socks (khuffayn).