Sura 26 Ash-Shu'ara' (The Poets), ayah 201

1. لَا يُؤْمِنُونَ بِهِ حَتَّىٰ يَرَوُا الْعَذَابَ الْأَلِيمَ

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

   26:201

Translation: Saheeh International