Musannaf Ibn Abi Shayba 35:308

Sharik narrated to us, from Ya'la ibn 'Ata, from Aws ibn Abi Aws, from his father, who said: I was with my father, and he reached one of the waters of the Bedouins. He performed ablution and wiped over his sandals. I asked him about that, and he said: I will not add anything for you beyond what I saw the Prophet, may Allah bless him and grant him peace, do.