Al-Kahf

But when they reached the junction between them, they forgot their fish, and it took its course into the sea, slipping away.

So when they had passed beyond it, [Moses] said to his boy, "Bring us our morning meal. We have certainly suffered in this, our journey, [much] fatigue."

He said, "Did you see when we retired to the rock? Indeed, I forgot [there] the fish. And none made me forget it except Satan - that I should mention it. And it took its course into the sea amazingly."

[Moses] said, "That is what we were seeking." So they returned, following their footprints.

And they found a servant from among Our servants [i.e., al-Khiḍr] to whom We had given mercy from Us and had taught him from Us a [certain] knowledge.

Moses said to him, "May I follow you on [the condition] that you teach me from what you have been taught of sound judgement?"

He said, "Indeed, with me you will never be able to have patience.

And how can you have patience for what you do not encompass in knowledge?"

[Moses] said, "You will find me, if Allāh wills, patient, and I will not disobey you in [any] order."

He said, "Then if you follow me, do not ask me about anything until I make to you about it mention [i.e., explanation]."