It is narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) went out to relieve himself, and he ordered Ibn Mas'ud (may Allah be pleased with him) to bring him three stones. He brought two stones and a piece of dung, so he (peace and blessings be upon him) threw away the dung and said: "This is filth; bring me a stone (in its place)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9915