Surah Al-Waqi'ah (The Inevitable Event), Verse 76

وَاِنَّهٗ لَقَسَمٌ لَّوْ تَعْلَمُوْنَ عَظِیْمٌ ۟

Wa innahoo laqasamul lawta'lamoona'azeem

“And that is indeed a mighty adjuration if ye but knew,-”

Quran 56:76 (Yusuf Ali Translation)