Quran 18:97 — The Cave (Al-Kahf)

Thus, they could not climb it, nor could they bore holes in it.

[18:96] "Bring to me masses of iron." Once he filled the gap between the two palisades, he said, "Blow." Once it was red hot, he said, "Help me pour tar on top of it."

[18:98] 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."