Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) was asked about purifying oneself (after relieving oneself), and he said: Can any of you not find three stones: two stones for the sides and one stone for the place from which the excrement exits?
Al-Tabarani recorded it in al-Mu'jam al-Kabir; its chain contains a narrator, Atiq bin Ya'qub al-Zubayri, about whom Imam Abu Zur'ah says: He memorized the "Muwatta" during the lifetime of Imam Malik.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الطهارة / 1048