Those who stayed away (from Tabuk expedition) rejoiced in their staying behind the Messenger of Allah; they hated to strive and fight with their properties and their lives in the cause of Allah, and they said: "March not forth in the heat." Say: "The fire of Hell is more intense in heat;" if only they could understand (81)So let them laugh a little and (they will) cry much as a recompense of what they used to earn (by committing sins)(82)

Allah admonishes the hypocrites who lagged behind from the battle of Tabuk with the Companions of the Messenger of Allah ﷺ, rejoicing that they remained behind after the Messenger ﷺ departed for the battle,

وَكَرِهُوا أَن يُجَاهِدُوا

(they hated to strive and fight), along with the Messenger ﷺ,

بِأَمْوَالِهِمْ وَأَنفُسِهِمْ فِي سَبِيلِ اللَّهِ وَقَالُوا

(with their properties and their lives in the cause of Allah, and they said), to each other,

لَا تَنفِرُوا فِي الْحَرِّ

("March not forth in the heat.") Tabuk occurred at a time when the heat was intense and the fruits and shades became delightful. This is why they said,

لَا تَنفِرُوا فِي الْحَرِّ

("March not forth in the heat") Allah said to His Messenger ﷺ,

قُلْ 

(Say) to them,

نَارُ جَهَنَّمَ

("The fire of Hell...), which will be your destination because of your disobedience,

أَشَدُّ حَرًّا

("...is more intense in heat;"), than the heat that you sought to avoid; it is even more intense than fire. Imam Malik narrated that Abu Az-Zinad said that Al-A'raj narrated that Abu Hurayrah said that the Messenger of Allah ﷺ said,

نَارُ بَنِي آدَمَ الَّتِي تُوقِدُونَهَا جُزْءٌ مِنْ سَبْعِينَ جُزْءًا مِنْ نَارِ جَهَنَّمَ

(The fire that the son of Adam kindles is but one part of seventy parts of the Fire of Jahannam.)

They said, "O Allah's Messenger! This fire alone is enough." He said,

فُضِّلَتْ عَلَيْهَا بِتِسْعَةٍ وَسِتِّينَ جُزْءًا

((Hellfire) was favored by sixty-nine parts.) The Two Sahihs collected this Hadith.

Al-A'mash narrated that Abu Ishaq said that An-Nu'man bin Bashir said that the Messenger of Allah ﷺ said,

إِنَّ أَهْوَنَ أَهْلِ النَّارِ عَذَابًا يَوْمَ الْقِيَامَةِ لِمَنْ لَهُ نَعْلَانِ وَشِرَاكَانِ مِنْ نَارِ جَهَنَّمَ يَغْلِي مِنْهُمَا دِمَاغُهُ كَمَا يَغْلِي الْمِرْجَلُ، لَا يَرَى أَنَّ أَحَدًا مِنْ أَهْلِ النَّارِ أَشَدُّ عَذَابًا مِنْهُ وَإِنَّهُ أَهْوَنُهُمْ عَذَابًا

(On the Day of Resurrection, the person who will receive the least punishment among the people of the Fire, wears two slippers made from the Fire of Jahannam causing his brain to boil, just as a pot boils. He thinks that none in the Fire is receiving a more severe torment than he, when in fact he is receiving the least torment.)

The Two Sahihs collected this Hadith. There are many other Ayat and Prophetic Hadiths on this subject. Allah said in His Glorious Book,

كَلَّا ۖ إِنَّهَا لَظَىٰ - نَزَّاعَةً لِّلشَّوَىٰ

(By no means! Verily, it will be the Fire of Hell. Taking away (burning completely) the scalp!)[70:15-16],

يُصَبُّ مِن فَوْقِ رُءُوسِهِمُ الْحَمِيمُ - يُصْهَرُ بِهِ مَا فِي بُطُونِهِمْ وَالْجُلُودُ - وَلَهُم مَّقَامِعُ مِنْ حَدِيدٍ - كُلَّمَا أَرَادُوا أَن يَخْرُجُوا مِنْهَا مِنْ غَمٍّ أُعِيدُوا فِيهَا وَذُوقُوا عَذَابَ الْحَرِيقِ

(Al-Hamim (boiling water) will be poured down over their heads. With it will melt (or vanish away) what is within their bellies, as well as (their) skins. And for them are hooked rods of iron (to punish them). Every time they seek to get away therefrom, from anguish, they will be driven back therein, and (it will be said to them): "Taste the torment of burning!")[22:19-22], and,

إِنَّ الَّذِينَ كَفَرُوا بِآيَاتِنَا سَوْفَ نُصْلِيهِمْ نَارًا كُلَّمَا نَضِجَتْ جُلُودُهُم بَدَّلْنَاهُمْ جُلُودًا غَيْرَهَا لِيَذُوقُوا الْعَذَابَ

(Surely, those who disbelieved in Our Ayat, We shall burn them in Fire. As often as their skins are roasted through, We shall change them for other skins that they may taste the punishment.)[4:56]

Allah said here,

قُلْ نَارُ جَهَنَّمَ أَشَدُّ حَرًّا ۚ لَّوْ كَانُوا يَفْقَهُونَ

(Say: "The fire of Hell is more intense in heat;" if only they could understand!) meaning, if they have any comprehension or understanding, they would have marched with the Messenger of Allah ﷺ during the heat, so as to save themselves from the Fire of Jahannam, which is much more severe.

Allah, the Exalted, then warns the hypocrites against their conduct,

فَلْيَضْحَكُوا قَلِيلًا

(So let them laugh a little...)

Ibn Abi Talhah reported that Ibn 'Abbas commented, "Life is short, so let them laugh as much as they like in it. But when life ends and they are returned to Allah, the Exalted and Most Honored, they will start crying forever without end."