Musannaf Ibn Abi Shayba 1:1895

Hafs narrated to us, from al-A’mash, from Abu Ishaq, from ‘Abd Khayr, from ‘Ali, who said: "If the religion were based on opinion, the bottom of the feet would be more deserving and entitled to be wiped than their tops. But I saw the Prophet, peace and blessings of Allah be upon him, wiping their tops."