(An-Nazi'ath) 79 : 8
قُلُوبٌ يَوْمَئِذٍ وَاجِفَةٌ
On that Day, hearts will be trembling in horror.
Since the Fujjar—Mujirims—are serving Satan, as explained in verses 7: 40 and 36: 59-62, on Doomsday their hearts will tremble with horror. See explanation 24: 37-38 and 68: 42-43.