Dr. Mustafa Khattab, the Clear Quran - Surah Al-Hijr, ayah 50

Translation of Surah Al-Hijr, ayah 50 (15:50)

وَأَنَّ عَذَابِي هُوَ ٱلۡعَذَابُ ٱلۡأَلِيمُ ٥٠
and that My torment is indeed the most painful.