Surah Al-Humazah 104:7

ٱلَّتِى تَطَّلِعُ عَلَى ٱلْأَفْـِٔدَةِ

Which mounts directed at the hearts.

Translation: Saheeh International

Tafsir

which peers over the hearts to burn them — the pain of which is much more severe than any other because of the delicate nature of the heart.

Excerpt from Tafsir al-Jalalayn, commentary on 104:7, via Quran.com. The reader has the full commentary and 9 more tafsirs.