Musannaf Ibn Abi Shayba 1:1931

Yahya ibn Adam narrated to us, from al-Hasan ibn Salih, from Nusayr ibn Dhu'luq, from Ibn Umar, that Sa'd ibn Malik wiped over the leather socks (khuffayn). Ibn Umar disapproved of that for him, so he mentioned it to his father. Sa'd ibn Malik said, "I am more knowledgeable than you."