Quran 18:98 — The Cave (Al-Kahf)

قالَ هٰذا رَحمَةٌ مِن رَبّى ۖ فَإِذا جاءَ وَعدُ رَبّى جَعَلَهُ دَكّاءَ ۖ وَكانَ وَعدُ رَبّى حَقًّا

He said, "This is mercy from my Lord. When the prophecy of my Lord comes to pass, He will cause the dam to crumble. The prophecy of my Lord is truth."

[18:97] Thus, they could not climb it, nor could they bore holes in it.

[18:99] At that time, we will let them invade with one another, then the horn will be blown, and we will summon them all together.