Quran 18:96 — The Cave (Al-Kahf)

"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."

[18:95] He said, "My Lord has given me great bounties. If you cooperate with me, I will build a dam between you and them.

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