Surah Al-Muzzammil 73:18

ٱلسَّمَآءُ مُنفَطِرٌۢ بِهِۦ ۚ كَانَ وَعْدُهُۥ مَفْعُولًا

The heaven will break apart therefrom; ever is His promise fulfilled.

Translation: Saheeh International

Tafsir

with the heaven being rent asunder thereon on that Day because of its severity. His promise exalted be He of the coming of that Day shall be fulfilled that is to say it will come to pass without doubt.

Excerpt from Tafsir al-Jalalayn, commentary on 73:18, via Quran.com. The reader has the full commentary and 9 more tafsirs.