ذٰلِكَ بِأَنَّهُم قالوا لَن تَمَسَّنَا النّارُ إِلّا أَيّامًا مَعدوداتٍ ۖ وَغَرَّهُم في دينِهِم ما كانوا يَفتَرونَ

That is because they say, "Never will the Fire touch us except for [a few] numbered days," and [because] they were deluded in their religion by what they were inventing.