Surah Al-Qamar 54:30

فَكَيْفَ كَانَ عَذَابِى وَنُذُرِ

And how [severe] were My punishment and warning.

Translation: Saheeh International

Tafsir

How then were My chastisement and My warnings? My warning them of chastisement before it was sent down? In other words it was justified. He explains it their chastisement by saying

Excerpt from Tafsir al-Jalalayn, commentary on 54:30, via Quran.com. The reader has the full commentary and 9 more tafsirs.