Sayyiduna Abu Hurayrah (may Allah be pleased with him) used to follow the Prophet (peace and blessings be upon him) with a vessel of water for his ablution and his call of nature. One day he (peace and blessings be upon him) found him and asked: "Who is this?" He said: I am Abu Hurayrah. He (peace and blessings be upon him) said: "Find me some stones so that I may clean myself, and do not bring me a bone or dung." I brought stones in my garment and placed them by his (peace and blessings be upon him) side, until he (peace and blessings be upon him) finished and stood up, and I followed him (peace and blessings be upon him).
I said: O Messenger of Allah, what is the matter with bones and dung? He (peace and blessings be upon him) said: "The delegation of Nasibin came to me and asked me for provision, so I prayed to Allah for them that they would not pass by any dung or bone without finding food on it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 524