The Cave
قَالَ أَمَّا مَن ظَلَمَ فَسَوْفَ نُعَذِّبُهُۥ ثُمَّ يُرَدُّ إِلَىٰ رَبِّهِۦ فَيُعَذِّبُهُۥ عَذَابًۭا نُّكْرًۭا
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.
Nearby ayahs help place verse 18:87 in sequence and meaning.
فَأَتْبَعَ سَبَبًا
So he followed a way
حَتَّىٰٓ إِذَا بَلَغَ مَغْرِبَ ٱلشَّمْسِ وَجَدَهَا تَغْرُبُ فِى عَيْنٍ حَمِئَةٍۢ وَوَجَدَ عِندَهَا قَوْمًۭا ۗ قُلْنَا يَـٰذَا ٱلْقَرْنَيْنِ إِمَّآ أَن تُعَذِّبَ وَإِمَّآ أَن تَتَّخِذَ فِيهِمْ حُسْنًۭا
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."
وَأَمَّا مَنْ ءَامَنَ وَعَمِلَ صَـٰلِحًۭا فَلَهُۥ جَزَآءً ٱلْحُسْنَىٰ ۖ وَسَنَقُولُ لَهُۥ مِنْ أَمْرِنَا يُسْرًۭا
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."
ثُمَّ أَتْبَعَ سَبَبًا
Then he followed a way