فَرِحَ المُخَلَّفونَ بِمَقعَدِهِم خِلافَ رَسولِ اللَّهِ وَكَرِهوا أَن يُجاهِدوا بِأَموالِهِم وَأَنفُسِهِم في سَبيلِ اللَّهِ وَقالوا لا تَنفِروا فِي الحَرِّ ۗ قُل نارُ جَهَنَّمَ أَشَدُّ حَرًّا ۚ لَو كانوا يَفقَهونَ

Those who remained behind rejoiced in their staying [at home] after [the departure of] the Messenger of Allah and disliked to strive with their wealth and their lives in the cause of Allah and said, "Do not go forth in the heat." Say, "The fire of Hell is more intensive in heat" - if they would but understand.