Musnad Ahmad 288:26

Al-Fadl ibn Dukayn narrated to us, he said: Sharik narrated to us, from Ya'la ibn 'Ata, from Aws ibn Abi Aws, he said: I was with my father at one of the waters of the Arabs, "and he performed ablution and wiped over his sandals." It was said to him [about that], so he said: "I do not add anything for you beyond what I saw the Messenger of Allah, may Allah bless him and grant him peace, doing."