Moses is Informed of a Wise Man
One day, Moses delivered such an impressive sermon that all who heard it were deeply moved. Someone in the congregation asked: "0 Messenger of Allah, is there another man on earth more learned than you?" Moses replied: "No!", believing so, as Allah had given him the power of miracles and honored him with the Torah.

However, Allah revealed to Moses that no man could know all there is to know, nor would one messenger alone be the custodian of all knowledge. There would always be another who knew what others did not. Moses asked Allah: "0 Allah, where is this man? I would like to meet him and learn from him." He also asked for a sign to this person's identity.

Allah instructed him to take a live fish in a water-filled vessel. Where the fish disappeared, he would find the man he sought. Moses set out on his journey, accompanied by a young man who carried the vessel with the fish. They reached a place where two rivers met and decided to rest there. Instantly, Moses fell asleep.

Moses Finds Al-Khidr
While he was asleep, his companion saw the fish wriggle out of the vessel into the river and swim away. However, he forgot to relate this incident to Moses. When he awoke, they continued their journey until they were exhausted and hungry. Moses asked for his morning meal. Only then did his companion recall that the fish they had brought with them had gotten away. Hearing this, Moses exclaimed: 'This is exactly what we are seeking!" They hurriedly retraced their steps to the place where the rivers met and where the fish had jumped out. There they found a man, his face partly covered with a hood. His bearing showed he was a saintly man. He was Al-Khidr, the guide.

Moses Finds Al-Khidr - Qur'anic
Allah the Almighty narrated: And (remember) when Moses said to his boy-servant: "I will not give up (traveling) until I reach the junction of the two seas or (until) I spend years and years in traveling."

But when they reached the junction of the two seas, they forgot their fish, and it took its way throught the sea as in a tunnel. So when they had passed further on (beyond that fixed place), Moses said to his boy-servant: "Bring us our morning meal; truly, we have suffered much fatigue in this, our journey."

He said: "Do you remember when we betook ourselves to the ock? I indeed forgot the fish, none but Satan made me forget to remember it. It took its course into the sea in a strange (way)!"

(Moses) said: "That is what we have been seeking." So they went back retracing their footsteps.

Then they found one of Our slaves, unto whom We had bestowed mercy from Us, and whom We had taught knowledge from Us. Surah 18: 60-65