Musannaf Ibn Abi Shayba 1:1625

Ghundar narrated to us, from Shu'bah, from Abu Salamah, that he heard Abu Nadrah narrating from Abu Sa'id, the freed slave of Abu Usayd, and he was a Bedouin, who said: When Abu Usayd would go to the privy, I would bring him water, and he would perform *istibra'* with it. Shu'bah said: Meaning he would perform *istinja'*.