Surah At-Taubah (The Repentance), Verse 81

فَرِحَ الْمُخَلَّفُوْنَ بِمَقْعَدِهِمْ خِلٰفَ رَسُوْلِ اللّٰهِ وَكَرِهُوْۤا اَنْ یُّجَاهِدُوْا بِاَمْوَالِهِمْ وَاَنْفُسِهِمْ فِیْ سَبِیْلِ اللّٰهِ وَقَالُوْا لَا تَنْفِرُوْا فِی الْحَرِّ قُلْ نَارُ جَهَنَّمَ اَشَدُّ حَرًّا لَوْ كَانُوْا یَفْقَهُوْنَ ۟

Farihal mukhallafoona bimaq'adihim khilaafa Rasoolil laahi wa karihooo ai yujaahidoo bi amwaalihim wa anfusihim fee sabeelil laahi wa qaaloo laa tanfiroo fil harr; qul Naaru jahannama ashaddu harraa; law kaanoo yafqahoon

“Those who were left behind (in the Tabuk expedition) rejoiced in their inaction behind the back of the Messenger of Allah: they hated to strive and fight, with their goods and their persons, in the cause of Allah: they said, "Go not forth in the heat." Say, "The fire of Hell is fiercer in heat." If only they could understand!”

Quran 9:81 (Yusuf Ali Translation)