Musannaf Ibn Abi Shayba 1:1643

Waki' narrated to us, from Isra'il, from Abu Ishaq, from Abu 'Ubaydah, from 'Abdullah, who said: The Messenger of Allah (may Allah bless him and grant him peace) went out for a need and said, "Seek three stones for me." I brought him two stones and a piece of dung. He took the two stones and threw away the dung, and said, "It is filth (rijs)."