The Prophet ﷺ went to relieve himself and instructed me to bring him three stones. I found two stones but could not find a third, so I picked up a piece of dried dung and brought it to him. He took the two stones and threw away the dung, saying, "This is filth."
أتى النبي ﷺ الغائط، فأمرني أن آتيه بثلاثة أحجار، فوجدت حجرين، والتمست الثالث فلم أجده، فأخذت روثة فأتيته بها، فأخذ الحجرين وألقى الروثة، وقال: هذا ركس.
Bukhari narrated it in the chapter on wudu (156), from Abu Naeem, who said, Zuhayr narrated to us, from Abu Ishaq, who said, "Abu Ubayda did not mention it, rather it was Abdul-Rahman bin Aswad, from his father, that he heard Abdullah (that is, Ibn Masud) say," and then he related the hadith.Bukhari said, and Ibrahim bin Yusuf said, from his father, from Abu Ishaq, "Abdul-Rahman narrated to me." End of quote.Regarding his saying "rikas," in another dialect this is "rijs" with a jeem, meaning filth. Abu Ubayd said, "It is similar to rajee (excrement). One says rakastu the thing and arkastuhu, meaning I returned it."Nasai (42) said, "Rikas is the food of the jinn."In another version found in Nasai (39), "He forbade that any of you cleanse himself with a bone or dung."In its chain of transmission is Abu Uthman bin Sunnah Khuzai, the narrator from Ibn Masud, who is "acceptable" because his narration is corroborated by others.