Musannaf Ibn Abi Shayba 1:1881

Abu al-Ahwas narrated to us, from Imran ibn Muslim, who said: We said to Nubatah al-Ju'fi—and he was the boldest of us toward Umar—"Ask him about wiping over the leather socks (khuffayn)." So he asked him, and he (Umar) said: "For the traveler, three days, and for the resident, a day and a night."