Musnad Abu Ya'la al-Mawsili 155:296

Uthman ibn Abi Shaybah narrated to us, Abu Dawud narrated to us, Aban ibn Abdullah al-Bajali narrated to us, from a freed slave of Abu Hurayrah, from Abu Hurayrah: That the Messenger of Allah (ﷺ) entered the privy, so I brought him water. He performed istinja (cleaned himself) and wiped his hand with soil, then he washed his hand.