It was narrated from 'Abdullah bin Mas'ud, that the Messenger of Allah (ﷺ) forbade cleaning oneself with bones or dung.
Sunan an-Nasa'i Book 1, Hadith 39
← Previous Hadith It was narrated from Al-Muhajir bin Qunfudh that he greeted the Prophet (ﷺ) with Salam while he was urinating, and he did not return the greeting until he had performed Wudu'. When he had performed Wudu' he returned the greeting.

Sunan an-Nasa'i Book 1, Hadith 38 Next Hadith → "I am like a father teaching you. When any one of you goes to Al-Khala' (the toilet), let him not face toward the Qiblah nor turn his back toward it, and let him not clean himself with his right hand." And he used to tell them to use three stones, and he forbade using dung or old bones.

Sunan an-Nasa'i Book 1, Hadith 40