Al-Imām al-Bukhārī - upon whom be mercy - narrates: Sulaymān ibn Ḥarb related to us; he said: Shuʿbah related to us, from Abū Muʿādh—and he is ‘Aṭā’ ibn Abī Maymūnah—who said:

I heard Anas ibn Mālik - may Allāh Almighty be content with him - say: Whenever the Messenger of Allāh ﷺ would go out to relieve himself, I and another young boy from among us would walk behind him, and with us was a leather water-skin containing water, which was carried for his purification.