The Cave - 18:26
"Say, "Allah knows better how long they stayed there."To Him belongs all the mysteries of the heavens and the earth. How beautiful is He, the All-Seeing! How excellent is He who Hears! They have no helper except Him. He does not associate anyone with His judgment."
Why did the youth take refuge in the cave?
The Cave/18:15
This people of ours have taken other gods besides Him. Should they not have proved by clear proof that they are gods? Who is more unjust than he who fabricates a lie against Allah?
The Cave/18:16
So since you have separated from them and those whom they serve besides Allah, take refuge in the cave. It may be that your Lord will shower upon you His mercy and prepare for you a favorable outcome in your affair.
The Cave/18:19
"So We woke them up so that they might ask one another. One of them asked, "How long did you stay?"They said, "We stayed for a day or a part of a day.""Your Lord knows better how long you stayed. Let us send one of you to the city with this money, and let him choose the food that is good and delicious, and bring you a provision. He should be careful not to attract anyone´s attention,"they added."
The Cave/18:20
If they recognize you, they will stone you or convert you to their religion, in which case you will never succeed.