(Ad-Dukhan) 44 : 50
إِنَّ هَٰذَا مَا كُنْتُمْ بِهِ تَمْتَرُونَ
Indeed, this is what you used to doubt.
After receiving Adhikr—the confirming Truth—the Fujjar who do not confirm that they are believers destined for Paradise are in doubt regarding unseen things which Adhikr predicts, and they are destined to be filled in Hell. See explanation 2: 147–148; 32: 20; and 42: 14.