Musannaf Ibn Abi Shayba 1:1933

Abu Bakr narrated to us, he said: Abu Bakr al-Hanafi narrated to us, from Usama bin Zayd, from Ishaq, the freed slave of Za'ida, that Sa'd bin Abi Waqqas came out from the privy, performed ablution, and wiped over his leather socks. It was said to him: "Do you wipe over them when you have come out from the privy?" He said: "Yes, when you have inserted the feet into the leather socks while they are pure, then wipe over them, and do not take them off except for major ritual impurity (janaba)."