Surah Al-Kahf, ayah 86

حَتَّىٰٓ إِذَا بَلَغَ مَغۡرِبَ ٱلشَّمۡسِ وَجَدَهَا تَغۡرُبُ فِي عَيۡنٍ حَمِئَةٖ وَوَجَدَ عِندَهَا قَوۡمٗاۖ قُلۡنَا يَٰذَا ٱلۡقَرۡنَيۡنِ إِمَّآ أَن تُعَذِّبَ وَإِمَّآ أَن تَتَّخِذَ فِيهِمۡ حُسۡنٗا ٨٦

Hattā idhā balagha maghribash-shamsi wajadahā taghrubu fī 'aynin hami'atin wawajada 'indahā qawman qulnā yādhal-qarnayni immā an tu'addhiba wa immā an tattakhidha fīhim husnā

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."