Surah Al-Hijr 15:50

وَأَنَّ عَذَابِى هُوَ ٱلْعَذَابُ ٱلْأَلِيمُ

And that it is My punishment which is the painful punishment.

Translation: Saheeh International

Tafsir

and that My chastisement of those who are disobedient is the painful chastisement.

Excerpt from Tafsir al-Jalalayn, commentary on 15:50, via Quran.com. The reader has the full commentary and 9 more tafsirs.