It is narrated from Sayyiduna Abu Ayyub al-Ansari (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you relieves himself, let him cleanse himself with three stones, for that is sufficient for him."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 4040