Surah Al-Anbya — Ayah 39 (21:39)

English translation (Saheeh International)

If those who disbelieved but knew the time when they will not avert the Fire from their faces or from their backs and they will not be aided...¹

1. - The completion of the sentence is understood to be "...they would not be asking in disbelief and ridicule to be shown the punishment."

Brief commentary

If these disbelieving rejecters of the resurrection were to know of the time when they will not be able to turn the hellfire away from their faces and backs, they would not be so hasty in seeking it. If only they were to know that there shall be no one to help relieve them of the punishment, and if only they were convinced of its reality, they would not be so hasty either.