Qur'an 18:86 · Al-Kahf

حَتَّىٰٓ إِذَا بَلَغَ مَغْرِبَ ٱلشَّمْسِ وَجَدَهَا تَغْرُبُ فِى عَيْنٍ حَمِئَةٍۢ وَوَجَدَ عِندَهَا قَوْمًۭا ۗ قُلْنَا يَٰذَا ٱلْقَرْنَيْنِ إِمَّآ أَن تُعَذِّبَ وَإِمَّآ أَن تَتَّخِذَ فِيهِمْ حُسْنًۭا

(86) 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."