I say, with Allah's guidance: It is disliked to the point of prohibition to cleanse oneself with bones, dung, and other impurities such as droppings and manure. As narrated from Ibn Mas'ud (may Allah be pleased with him) in a marfu' (elevated) hadith: "Do not cleanse yourselves with dung or bones, for they are the provision of your brothers from the jinn," in Sahih Ibn Hibban 1: 44. Also, because when the Prophet (peace be upon him) asked Abdullah Ibn Mas'ud about stones for cleansing, he brought him two stones and dung. The Prophet took the stones and discarded the dung, explaining that it was impure, saying: It is filth. If one were to cleanse with a bone, purification would be achieved, albeit with dislike, because what matters is cleanliness, which is achieved; and because the prohibition is due to a reason in something else, it does not prevent purification: like cleansing with someone else's cloth or water. See: Bada'i al-Sana'i 1/18, Radd al-Muhtar 1/339, and Allah knows best.