Until, when he reached the setting of the sun [i.e., the west], he found it [as if] setting in a body of dark water,1 and he found near it a people. We [i.e., Allāh] said, "O Dhul-Qarnayn, either you punish [them] or else adopt among them [a way of] goodness."
And he travelled on earth until he reached the end of the land towards the setting place of the sun, seeing it as though it was setting in a hot spring of black clay. And he found an unbelieving people by the setting place of the sun. So I said to him, to test him: “O Dhu’l-Qarnayn, you can either punish these people by killing them or through other means, or you can be good to them”.