They do not believe until they see a tragic suffering.
Sayyed Abbas Sadr-Ameli
(But) they will not believe in it until they see the painful punishment
Al-muntakhab fi tafsir al-Qur'an al-Karim
Who shall not acknowledge it as the truth personified until they have had the wind in their faces and they are face to face with the promised punishment here, at the hands of the Muslims or with the torment laid upon the damned Hereafter