Musnad Ahmad 8:178

Yazid ibn Harun narrated to us, Al-Hajjaj ibn Artah informed us, from Yahya ibn Ubayd al-Bahrani, from Muhammad ibn Sa’d, who said—and he was performing ablution at the corner: "He came out to us one day from relieving himself, so he performed ablution and wiped over his leather socks." We were amazed and said, "What is this?" He said, "My father narrated to me that he saw the Messenger of Allah, may Allah bless him and grant him peace, do the same as I have done."