Al-Waqi'ah - 56:76

وَإِنَّهُ لَقَسَمٌ لَّوْ تَعْلَمُونَ عَظِيمٌ
[56:76]
And most surely it is a very great oath if you only knew;
And that is indeed a mighty adjuration if ye but knew,-
And lo! that verily is a tremendous oath, if ye but knew -