Al-Imām al-Bukhārī - upon whom be mercy - narrates: Abū al-Walīd Hishām ibn ‘Abd al-Malik related to us; he said: Shu’bah related to us, from Abū Mu’ādh—whose name is ‘Aṭā’ ibn Abī Maymūnah—who said:

I heard Anas ibn Mālik - may Allāh Almighty be content with him - say that whenever the Messenger of Allāh ﷺ went out to relieve himself, I and another young boy would accompany him, carrying a vessel of water, and he ﷺ would cleanse himself with it (perform istinjā’).