Surah Al-Hijr, ayah 50

وَأَنَّ عَذَابِي هُوَ ٱلۡعَذَابُ ٱلۡأَلِيمُ ٥٠

Wa anna 'adhābī huwal-'adhābul-alīm

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