The Cave
حَتَّىٰٓ إِذَا بَلَغَ مَغْرِبَ ٱلشَّمْسِ وَجَدَهَا تَغْرُبُ فِى عَيْنٍ حَمِئَةٍ وَوَجَدَ عِندَهَا قَوْمًا ۗ قُلْنَا يَـٰذَا ٱلْقَرْنَيْنِ إِمَّآ أَن تُعَذِّبَ وَإِمَّآ أَن تَتَّخِذَ فِيهِمْ حُسْنًا
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."
Nearby ayahs help place verse 18:86 in sequence and meaning.
إِنَّا مَكَّنَّا لَهُۥ فِى ٱلْأَرْضِ وَءَاتَيْنَـٰهُ مِن كُلِّ شَىْءٍ سَبَبًا
Indeed We established him upon the earth, and We gave him to everything a way.
فَأَتْبَعَ سَبَبًا
So he followed a way
قَالَ أَمَّا مَن ظَلَمَ فَسَوْفَ نُعَذِّبُهُۥ ثُمَّ يُرَدُّ إِلَىٰ رَبِّهِۦ فَيُعَذِّبُهُۥ عَذَابًا نُّكْرًا
He said, "As for one who wrongs, we will punish him. Then he will be returned to his Lord, and He will punish him with a terrible punishment.
وَأَمَّا مَنْ ءَامَنَ وَعَمِلَ صَـٰلِحًا فَلَهُۥ جَزَآءً ٱلْحُسْنَىٰ ۖ وَسَنَقُولُ لَهُۥ مِنْ أَمْرِنَا يُسْرًا
But as for one who believes and does righteousness, he will have a reward of Paradise, and we will speak to him from our command with ease."