Musnad Ahmad Hadith 21120

It is narrated from Ibn Abbas (may Allah be pleased with them both) with reference to Ubayy bin Ka'b (may Allah be pleased with him) that I heard the Holy Prophet (ﷺ) say: Once Musa (peace be upon him) was standing and delivering a sermon before the Children of Israel. After the sermon ended, a man asked, "Who is the most knowledgeable among the people?" Musa (peace be upon him) replied, "I am the most knowledgeable." Allah disliked that Musa did not attribute knowledge to Allah, so revelation was sent to Musa (peace be upon him) that among My servants there is a servant who is more knowledgeable than you. Musa (peace be upon him) said, "O Lord, how can I meet him?" He was commanded, "Take a (roasted) fish in a basket with you (and set out on your journey). Where the fish is lost, you will find that person." Musa (peace be upon him) took a fish, placed it in the basket, and set out, and the incident occurred as Allah has described, until finally, after traveling, they reached a village. They asked the villagers for food, but they refused to host them. Then Khidr (peace be upon him) explained to them the reality of the incident with the boat, saying that he damaged it because of the king, so that when he passed by, he would not seize it. As for the boy, he was naturally a disbeliever, and his parents were very affectionate towards him; if he had lived, he would have led them into rebellion and disobedience. As for the wall, it belonged to two orphan boys in the city.