Musannaf Ibn Abi Shayba 1:1626

Ibn Dukayn narrated to us, from Qurrah, from Budayl al-Uqayli, from Mutarrif ibn Abdullah ibn al-Shikhkhir, who said: A Bedouin narrated to me, saying: I accompanied Abu Dharr, and all of his traits pleased me, except for one trait. I said: What is it? He said: When he would exit the privy, he would perform istinja (cleaning himself with water).