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

This is because they say, “The Fire will touch us only for a number of days.” What they used to invent deceived them in their religion.