Al-Imām al-Bukhārī narrates that Abū al-Qāsim Khālid ibn Khalī related to us; he said: Muḥammad ibn Ḥarb narrated to us. He said: al-Awzāʿī said: al-Zuhrī informed us, from ʿUbaydullāh ibn ʿAbdullāh ibn ʿUtbah ibn Masʿūd,

from Ibn ‘Abbās (may Allāh be content with them both), who said: There was a discussion between him and Ḥurr ibn Qays al-Fazārī regarding the companion of Mūsā (peace be upon him). Then Ubayy ibn Ka’b (may Allāh Almighty be content with him) passed by them. Ibn ‘Abbās called him and said: “There has been a discussion between me and this companion of mine regarding the companion of Mūsā, about whom Mūsā had asked the way to meet.” Ubayy said: “Yes, I heard the Prophet ﷺ mention him. He said that while Mūsā was among a gathering of the Children of Isrā’īl, a man came and said: ‘Do you know of anyone more knowledgeable than you?’ Mūsā said: ‘No.’ So Allāh, Mighty and Majestic, revealed to Mūsā: ‘Yes—Our servant al-Khiḍr is more knowledgeable.’ Then Mūsā asked about the way to meet him, so Allāh made the fish a sign for him, and it was said to him: ‘Wherever you lose the fish, return from there.’ Soon he met him. Mūsā (peace be upon him) then followed the trace of the fish by the sea. Then Mūsā’s attendant said to him: ‘Did you see? When we rested by the rock, I forgot to mention the fish—and none made me forget to mention it except Shayṭān.’ (al-Kahf: 61) Mūsā said: ‘That is what we were seeking.’ So they returned, retracing their footsteps.” (al-Kahf: 64) Then they found al-Khiḍr, and thereafter occurred the event which Allāh has mentioned in His Book.