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) said: "Cleansing oneself after relieving oneself (istinja) is with three stones in which there is no dung."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3712