On the Day when that will be heated in the fire of Hell and with it will be branded their foreheads, their flanks, and their backs, (and it will be said unto them) "This is the treasure which you hoarded for yourselves. Now taste of what you used to hoard."

These words will be said to them as a way of admonishing, criticizing and mocking them.

Allah also said;

ثُمَّ صُبُّواْ فَوْقَ رَأْسِهِ مِنْ عَذَابِ الْحَمِيمِ

ذُقْ إِنَّكَ أَنتَ الْعَزِيزُ الْكَرِيمُ

Then pour over his head the torment of boiling water. "Taste you (this)! Verily, you were (pretending to be) the mighty, the generous!" (44:48-49)

There is a saying that goes,

"He who covets a thing and prefers it to Allah's obedience, will be punished with it."

Because hoarding money was better to these people than Allah's pleasure, they were punished with it.

For instance, Abu Lahab, may Allah curse him, was especially active in defying the Messenger of Allah, and his wife was helping him in this regard. Therefore, on the Day of Resurrection, she will help in punishing him, for there will be a twisted rope of palm fiber on her neck. She will be gathering wood from the Fire and throwing it on him so that his torment is made harder by the hand of someone whom he used to care for in this life.

Likewise, money was precious to those who hoarded it in this life. Therefore, money will produce the worst harm for them in the Hereafter, when it will be heated in the Fire of Jahannam, whose heat is quiet sufficient, and their forehead, sides and back will be branded with it.

Imam Abu Jafar Ibn Jarir recorded that Thawban said that the Messenger of Allah used to declare,

مَنْ تَركَ بَعْدَهُ كَنْزًا مُثِّلَ لَهُ يَوْمَ الْقِيَامَةِ شُجَاعًا أَقَرَعَ لَهُ زَبِيبَتَانِ يَتْبَعُهُ وَيَقُولُ وَيْلَكَ مَا أَنْتَ فَيَقُولُ أَنَا كَنْزُكَ الَّذِي تَرَكْتَهُ بَعْدكَ وَلَا يَزَالُ يَتْبَعُهُ حَتَّى يُلْقِمَهُ يَدَهُ فَيَقْضِمَهَا ثُمَّ يَتْبَعُهَا سَايِرَ جَسَدِه

Whoever leaves a treasure behind (on which he did not pay the Zakah), then on the Day of Resurrection his wealth will be made like a bald-headed poisonous male snake with two black spots over the eyes. The snake will follow him, and he will say, `Woe to you! Who are you!' The snake will say, `I am your treasure that you left behind,' and will keep following him until the man gives it his hand; the snake will devour it and then devour his whole body. 

Ibn Hibban also collected this Hadith in his Sahih.

Part of this Hadith was also collected in the Two Sahihs from Abu Hurayrah.

In his Sahih, Muslim recorded from Abu Hurayrah that the Messenger of Allah said,

مَا مِنْ رَجُلٍ لَاا يُوَدِّي زَكَاةَ مَالِهِ إِلاَّ جُعِلَ لَهُ يَوْمَ الْقِيَامَةِ صَفَايِحُ مِنْ نَارٍ فَيُكْوَى بِهَا جَنْبُهُ وَجَبْهَتُهُ وَظَهْرُهُ فِي يَوْمٍ كَانَ مِقْدَارُهُ خَمْسِينَ أَلْفَ سَنَةٍ حَتَّى يُقْضَى بَيْنَ الْعِبَادِ ثُمَّ يُرَى سَبِيلُهُ إِمَّا إِلَى الْجَنَّةِ وَإِمَّا إِلَى النَّار

Every man who does not pay the Zakah due on his money, then on the Day of Resurrection, his side, forehead and back will be branded with rods made of fire on a Day the length of which is fifty thousand years, until when the servants will be judged; that man will be shown his destination, either to Paradise or the Fire.

In the Tafsir of this Ayah, Al-Bukhari recorded that Zayd bin Wahb said,

"I passed by Abu Dharr in the area of Rabadhah and asked him, `What made you reside in this area?'

He said, `We were in Ash-Sham when I recited this Ayah,

وَالَّذِينَ يَكْنِزُونَ الذَّهَبَ وَالْفِضَّةَ وَلَا يُنفِقُونَهَا فِي سَبِيلِ اللّهِ فَبَشِّرْهُم بِعَذَابٍ أَلِيمٍ


And those who hoard up gold and silver and spend them not in the way of Allah, announce unto them a painful torment.

Mu`awiyah said, `This Ayah is not about us, it is only about the People of the Book.'

So I (Abu Dharr) said, `Rather, it is about us and them.