Al-Kahf 86

حَتَّىٰٓ إِذَا بَلَغَ مَغْرِبَ ٱلشَّمْسِ وَجَدَهَا تَغْرُبُ فِى عَيْنٍ حَمِئَةٍ وَوَجَدَ عِندَهَا قَوْمًا قُلْنَا يَٰذَا ٱلْقَرْنَيْنِ إِمَّآ أَن تُعَذِّبَ وَإِمَّآ أَن تَتَّخِذَ فِيهِمْ حُسْنًا ﴿٨٦﴾

Hatta itha balagha maghriba alshshamsi wajadaha taghrubu fee AAaynin hamiatin wawajada AAindaha qawman qulna ya tha alqarnayni imma an tuAAaththiba waimma an tattakhitha feehim husnan

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 (Allah) said (by inspiration): "O Dhul-Qarnain! Either you punish them, or treat them with kindness." The Noble Quran