Surah Al-Kahf (The Cave), Verse 86

حَتّٰۤی اِذَا بَلَغَ مَغْرِبَ الشَّمْسِ وَجَدَهَا تَغْرُبُ فِیْ عَیْنٍ حَمِئَةٍ وَّوَجَدَ عِنْدَهَا قَوْمًا قُلْنَا یٰذَا الْقَرْنَیْنِ اِمَّاۤ اَنْ تُعَذِّبَ وَاِمَّاۤ اَنْ تَتَّخِذَ فِیْهِمْ حُسْنًا ۟

Hattaaa izaa balagha maghribash shamsi wajadahaaa taghrubu fee 'aynin hami'a tinw wa wajada 'indahaa qawmaa; qulnaa yaa Zal Qarnaini immaaa an tu'az ziba wa immaaa an tattakhiza feehim husnaa

“Until, when he reached the setting of the sun, he found it set in a spring of murky water: Near it he found a People: We said: "O Zul-qarnain! (thou hast authority,) either to punish them, or to treat them with kindness."”

Quran 18:86 (Yusuf Ali Translation)