Musannaf Ibn Abi Shayba 1:1647

Abu Bakr narrated to us, from Hatim ibn Isma'il, from Ja'far, from Nafi', who said: Ibn 'Umar used not to perform *istinja* (cleaning oneself after defecation) with water. I used to bring him stones from the *Harrah* (volcanic rocky area). When they were filled, I would go out with them and discard them, then I would insert others in their place.