Surah Al-Kahf, Verse 86
حَتَّىٰٓ إِذَا بَلَغَ مَغْرِبَ ٱلشَّمْسِ وَجَدَهَا تَغْرُبُ فِى عَيْنٍ حَمِئَةٍۢ وَوَجَدَ عِندَهَا قَوْمًۭا ۗ قُلْنَا يَٰذَا ٱلْقَرْنَيْنِ إِمَّآ أَن تُعَذِّبَ وَإِمَّآ أَن تَتَّخِذَ فِيهِمْ حُسْنًۭا
Translation — Sahih International
Until, when he reached the setting of the sun, he found it [as if] setting in a spring of dark mud, and he found near it a people. Allah said, "O Dhul-Qarnayn, either you punish [them] or else adopt among them [a way of] goodness."
Source
Kur'an-ı Kerim, Kehf Suresi 18:86
https://kuran.diyanet.gov.tr/mushaf/kuran-meal-2/18-suresi-86-ayet