Musannaf Ibn Abi Shayba 1:1887

Hushaym narrated to us, he said: Yunus informed us, from al-Hakam ibn al-A'raj, who said: I asked Ibn Umar about wiping over the leather socks (khuffayn). He said: "Sa'd and I differed regarding that while we were at Jalula. Sa'd said: 'Wipe over them,' but I disapproved of that. When we arrived to Umar, I mentioned that to him." He said: "I said: 'O Commander of the Believers, he says to wipe over them after the ritual impurity (hadath).' Umar said: 'Except after defecation (khara'ah), except after the ritual impurity (hadath).'"