Musannaf Ibn Abi Shaybah 200 — Those who said: wash your feet

Muhammad bin Mahmud said: The Prophet (peace and blessings be upon him) saw a blind Companion performing ablution. He washed his face and his hands, and the Prophet (peace and blessings be upon him) said to him: "Wash the undersides of your feet as well." So, in compliance with this instruction, he washed the undersides of his feet as well.