Musannaf Ibn Abi Shayba 1:1886

Hushaym narrated to us, he said: Husayn informed us, from Muharib, from Ibn Umar, who said: Sa'd and I differed at al-Qadisiyyah regarding wiping over the leather socks (khuffayn). Sa'd said, "Wipe over them," and I denied that. When we came to Umar ibn al-Khattab, Sa'd mentioned that to him and said to him, "Do you not see that Ibn Umar denies wiping over the leather socks?" I said, "O Commander of the Faithful, Sa'd says to wipe over them after the hadath (minor ritual impurity)." Umar said, "Except after the hadath? Except after defecation?"