Al-Kahf 18:86

until when he reached the far west, he found the sun setting in a dark body of water, and he found some people nearby. We said, “O Dhul-Qarnayn, either punish them or treat them with kindness.”

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,[795] 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."

[795] Another meaning is "a body of hot water."

86. Until, when he reached the setting place of the sun, he found it setting in a spring of black muddy (or hot) water. And he found near it a people. We (Allâh) said (by inspiration): "O Dhul-Qarnain! Either you punish them, or treat them with kindness."

Till, when he reached the setting-place of the sun, he found it setting in a muddy spring, and found a people thereabout. We said: O Dhu'l-Qarneyn! Either punish or show them kindness.