Musannaf Ibn Abi Shayba 1:2038

Hushaym narrated to us, from Yunus, from al-Hasan, who said: When he would enter the mosque during rain, he would look at his leather socks. If there was a little mud on them, he would wipe them, then enter and pray. If there was a lot of mud on them, he would take them off and order that they be washed.