Sayyiduna Ibn Mas'ud (may Allah be pleased with him) says: I went out with the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) ordered me to bring three stones. I brought two stones and a piece of dung, so he (peace and blessings be upon him) took the two stones, threw away the dung and said: "This is filth."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9920