Until, when he reached the setting of the sun, he found it (18:86)

Almuntakhab Fi Tafsir Alquran Alkarim

He took the lead in an expedition toward he west until he reached a body of water -said to be the Atlantic Ocean, or more likely a mirky land abounding in swamps– where -he thought when viewing the horizon- the sun sets and where he found a -disorderly and unruly- people over whom We gave him authority. We left to him the manner of dealing with them. Either you punish them, We said or show them kindness

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(18:86) till he reached the limit where the sun set, *63 and found it setting in black waters, *64 and there he saw a people. We said to him, "O Zul-Qarnain! you have the power to punish them and also the option to treat them generously". *65

Until, when he reached the setting of the sun, he found it meaning

*63) "The limit where the sun set" does not mean the "place" of the setting of the sun. According to Ibn Kathir, it means that he marched to the West conquering one country after the other till he reached the last boundary of the land, beyond which there was ocean.
*64) "He found the sun setting in black muddy waters of the sea": if ZulQarnain was Cyrus, then that place would be the western limit of Asia Minor and the "black waters" would be the Aegean Sea. This interpretation is supported by the use of the word "`ain"instead of "bahr" in the Qur'an.
<*65) "We said to him" does not necessarily mean that Allah directly revealed to him these words, and that Z, ul-Qarnain was a Prophet or was the one who received inspiration from Allah, and the same is the reasonable conjecture. This concerns the time when Zul-Qarnain had taken possession of the land as a conqueror and the conquered people were utterly at your mercy. Then Allah posed a question before his conscience, as if to say, "Now is the time of your trial. These people are utterly at your mercy, and you have the option either to behave unjustly towards them or to treat them generously."
 

Until, when he reached the setting of the sun, he found it meaning in Urdu

حتیٰ کہ جب وہ غروب آفتاب کی حَد تک پہنچ گیا تو اس نے سورج کو ایک کالے پانی میں ڈوبتے دیکھا اور وہاں اُسے ایک قوم ملی ہم نے کہا "اے ذوالقرنین، تجھے یہ مقدرت بھی حاصل ہے کہ ان کو تکلیف پہنچائے اور یہ بھی کہ اِن کے ساتھ نیک رویّہ اختیار کرے"