Surah At-Takathur 102:5

كَلَّا لَوْ تَعْلَمُونَ عِلْمَ ٱلْيَقِينِ

No! If you only knew with knowledge of certainty...

Translation: Saheeh International

Tafsir

No indeed! — verily — Were you to know with certain knowledge the consequences of your vainglory you would not preoccupy yourselves with it for

Excerpt from Tafsir al-Jalalayn, commentary on 102:5, via Quran.com. The reader has the full commentary and 9 more tafsirs.