Quran 18:95 — The Cave (Al-Kahf)

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

[18:94] They said, "O Zul-Qarnain, Gog and Magog are corruptors of the earth. Can we pay you to create a barrier between us and them?"

[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."