Musnad Ahmad 920:9

Bahz ibn Asad narrated to us, Sufyan ibn 'Uyaynah narrated to me—dictating it to me—from 'Amr, from Sa'id ibn Jubayr, who said: I said to Ibn 'Abbas—'Abdullah said: My father said: "I wrote it from Bahz and Ibn 'Uyaynah"—that Nawf claims that Musa is not the companion of Al-Khidr. He said: So he said: "The enemy of Allah has lied. Ubayy ibn Ka'b narrated to us from the Prophet, peace and blessings of Allah be upon him, who said: 'Musa stood up to deliver a sermon to the Children of Israel, and he was asked: "Who is the most learned of the people?" He said: "I am." Allah rebuked him because he did not attribute knowledge to Him. Allah said: "Rather, I have a servant at the junction of the two seas who is more learned than you." He said: "O my Lord, how can I reach him?" He said: "Take a fish and put it in a basket, then set out. Wherever you lose it, he is there." So Musa set out, and with him was his young man, walking until they reached the rock. Musa slept, and the fish thrashed in the basket and escaped, falling into the sea. Allah held back the flow of the water for it, like an arch, and it became a tunnel for the fish.'" Sufyan said: "He joined his thumb and index finger and spread them apart." He said: "They continued on until the next day. Musa said to his young man: 'Bring us our morning meal; indeed, we have suffered much fatigue from this journey of ours.' [Al-Kahf: 62]." He said: "He did not feel the fatigue until he had passed the place he was commanded to reach. 'He said: That is what we were seeking.' [Al-Kahf: 64]. So they returned, retracing their footsteps, following their tracks." He said: "The trace of the fish was a wonder for Musa, and for the fish, it was a tunnel." Then he mentioned the rest of the hadith.