And in this is evidence that washing both feet is obligatory, not wiping over them.

Hazrat Abu Wa'il Shaqiq bin Salamah narrates that I saw Sayyiduna Uthman bin Affan (may Allah be pleased with him) performing ablution three times each, and wiping over his head and the inner and outer parts of both his ears, and washing both his feet three times each, and washing his fingers, and combing through his beard, and washing his face, and he said that I saw the Messenger of Allah (peace and blessings be upon him) performing ablution in this manner as you have seen me performing it.