Sahih Bukhari Volume 001, Book 003, Hadith Number 078.
Narated By Ibn 'Abbas : That he differed with Hur bin Qais bin Hisn Al-Fazari regarding the companion of the Prophet Moses. Meanwhile, Ubai bin Ka'b passed by them and Ibn 'Abbas called him saying, "My friend (Hur) and I have differed regarding Moses' companion whom Moses asked the way to meet. Have you heard Allah's Apostle mentioning something about him? Ubai bin Ka'b said: "Yes, I heard the Prophet mentioning something about him (saying) while Moses was sitting in the company of some Israelites, a man came and asked him: "Do you know anyone who is more learned than you? Moses replied: "No." So Allah sent the Divine Inspiration to Moses: '...Yes, Our slave Khadir is more learned than you. Moses asked Allah how to meet him (Al-Khadir). So Allah made the fish a sign for him and he was told when the fish was lost, he should return (to the place where he had lost it) and there he would meet him (Al-Khadir). So Moses went on looking for the sign of the fish in the sea. The servant-boy of Moses said: 'Do you remember when we betook ourselves to the rock, I indeed forgot the fish, none but Satan made me forget to remember it. On that Moses said, 'That is what we have been seeking.' So they went back retracing their footsteps, and found Kha,dir. (and) what happened further about them is narrated in the Holy Qur'an by Allah." (18.54 up to 18.82)