Al-Imām al-Bukhārī - upon whom be mercy - narrates: Abū Nu’aym related to us; he said: Zuhayr related to us, from Abū Isḥāq. He said: Abū ‘Ubaydah did not mention this ḥadīth, but ‘Abd al-Raḥmān ibn al-Aswad narrated from his father that he heard

‘Abdullāh ibn Mas’ūd - may Allāh Almighty be content with him - say: The Messenger of Allāh ﷺ came to relieve himself and commanded me to bring him three stones. I found two stones, but when I searched for a third stone I did not find one, so I took a piece of dung and brought it to him ﷺ. He ﷺ took the two stones and cast aside the dung, saying: “This is impure.”

And Ibrāhīm ibn Yūsuf narrated from his father, from Abū Isḥāq, that ‘Abd al-Raḥmān related this ḥadīth to him.