Surah Al-Waqi'ah 56:76

وَإِنَّهُۥ لَقَسَمٌ لَّوْ تَعْلَمُونَ عَظِيمٌ

And indeed, it is an oath - if you could know - [most] great.

Translation: Saheeh International

Tafsir

And indeed it the swearing by these setting-places of stars is a tremendous oath if you only knew — if you were people of deep knowledge you would realise the magnitude of this oath.

Excerpt from Tafsir al-Jalalayn, commentary on 56:76, via Quran.com. The reader has the full commentary and 9 more tafsirs.