Surah Al-Kahf 18:98

قَالَ هَـٰذَا رَحْمَةٌ مِّن رَّبِّى ۖ فَإِذَا جَآءَ وَعْدُ رَبِّى جَعَلَهُۥ دَكَّآءَ ۖ وَكَانَ وَعْدُ رَبِّى حَقًّا

[Dhul-Qarnayn] said, "This is a mercy from my Lord; but when the promise of my Lord comes [i.e., approaches], He will make it level, and ever is the promise of my Lord true."

Translation: Saheeh International

Tafsir

Said he Dhū’l-Qarnayn ‘This namely the barrier the ability to make it is a mercy from my Lord a grace from Him because it prevents them from coming forth. But when the promise of my Lord comes to pass the promise of their coming forth which will be near the time of the Resurrection He will level it pulverised and …

Excerpt from Tafsir al-Jalalayn, commentary on 18:98, via Quran.com. The reader has the full commentary and 9 more tafsirs.