Musannaf Ibn Abi Shayba 3:5514

Waki’ narrated to us, he said: Yazid bin Ibrahim al-Tustari narrated to us, from al-Husayn, he said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Examine your sandals; if one of you sees filth on them, let him wipe it off, and otherwise, let him pray in them."