Quran 18:83-98

[Prophet], they ask you about Dhu ’l-Qarnayn. Say, ‘I will tell you something about him.’ We established his power in the land, and gave him the means to achieve everything He travelled on a certain road then, when he came to the setting of the sun, he found it [seemed to be] setting into a muddy spring. Nearby he found some people and We said, ‘Dhu ’l-Qarnayn, you may choose [which of them] to punish or show kindness to.’ He answered, ‘We shall punish those who have done evil, and when they are returned to their Lord He will punish them [even more] severely while those who believed and did good deeds will have the best of rewards: we shall command them to do what is easy for them.’ He travelled on then, when he came to the rising of the sun, he found it rising on a people for whom We had provided no shelter from it And so it was: We knew all about him He travelled on then, when he reached a place between two mountain barriers, he found beside them a people who could barely understand him They said, ‘Dhu ’l-Qarnayn, Gog and Magog are ruining this land. Will you build a barrier between them and us if we pay you a tribute?’ He answered, ‘The power my Lord has given me is better than any tribute, but if you lend me your strength, I will put up a fortification between you and them bring me lumps of iron!’ and then, when he had filled the gap between the two mountainsides [he said], ‘Work your bellows!’ and then, when he had made it glow like fire, he said, ‘Bring me molten metal to pour over it!’ Their enemies could not scale the barrier, nor could they pierce it and he said, ‘This is a mercy from my Lord. But when my Lord’s promise is fulfilled, He will raze this barrier to the ground: my Lord’s promise always comes true.’