It is narrated from Sayyiduna Khuzaymah bin Thabit (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) was asked about cleansing oneself after relieving oneself (istinja), and he (peace and blessings be upon him) said: "Three stones in which there is no dung."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3711