And O Muhammad, they ask you about Zul-Qarnain:61 tell them, “I am going to recite to you an account of him.”62 We had established his power on the Earth and had provided him with every kind of ways and means. At first, he made preparations for an expedition (to the West and marched on) till he reached the limit where the sun set,63 and found it setting in black waters,64 and there he saw a people. We said to him, “O Zul-Qarnain! You have the power to punish them and also the option to treat them generously.”65 He said, “We will punish that one of them who will commit iniquity: then he shall be returned to his Lord and He will inflict on him a grievous torment: And as for the one, who will believe and do righteous deeds, there is a generous recompense and We will prescribe for him easy tasks.” Then he made preparations (for another expedition and marched on) till he reached the limit where the sun rose. There he saw the sun rising on a people, whom We had not given any shelter from sun shine.66 This was their condition and We know well whatever Zul-Qarnain possessed. Then he made preparations (for another expedition and marched on) till he reached between two mountains,67 where he found a people who could hardly understand any language.68 They said, “O Zul-Qarnain, Gog and Magog69 spread chaos in this land; should we then pay a tribute to you so that you may build a bulwark between us and them” He said, “What my Allah has granted me is more than enough. You should help me only with manual labor and I will build a barrier between you and them.70 Come, bring sheets of iron for me. "When he had filled the space between the two mountains, he said to the people, “Now, ply your bellows.” They did so till that (iron-wall) became red-hot and he said, “Now let me pour molten brass upon it.” This was such a barrier that Gog and Magog could not scale over it, nor were they able to dig through it. Zul-Qarnain said, “This is a mercy from my Lord; but when the time of my Lord's promise shall come, He will level it to dust71 and the promise of my Lord is true.”72 And on that Day,73 We will let loose the people to come close together tumultuously (like the waves of an ocean), and the trumpet shall be blown, and We will gather together all mankind. On that Day Hell shall be brought before the unbelievers who had become blind to My admonition and turned a deaf ear to it.