26:201

لَا يُؤْمِنُونَ بِهِ حَتَّىٰ يَرَوُا الْعَذَابَ الْأَلِيمَ

Transliteration:

La yu/minoona bihi hatta yarawoo alAAathaba al-aleema

Word by Word:

Not they will believe in it until they see the punishment [the] painful.

Translations:

they will not believe in it till they behold the grievous suffering

They will not believe in it until they see the grievous Penalty;

They will not believe in it till they behold the painful doom,

They will not believe in it till they see the painful chastisement:

They will not believe in it until they see the painful punishment.