Zaqqum tree as the caution for the sinner
The Zaqqum Tree, is the tree that is in Hell. Yes the tree is as hard as a rock and its prick like a concrete nail. It is clearly written in the Qur'an and one of them:
information in surat al-Waqiah,
ثم إنكم أيها الضالون المكذبون. لآكلون من شجر من زقوم
Then verily, you who deny astray () will indeed eat the tree of zaqqum, and will fill your stomach with it. (Surah al-Waqi'ah: 51 - 53).
Information about the zaqqum tree is also described in al-Isra verse 60. Allah Subhana Wa Ta'ala calls this tree a curse tree.
"We do not make the dream that We have shown you, but as a test for man and (so) a damned tree in the Qur'an. And We frighten them, but such is only add to their wickedness. " (Surah al-Isra: 60).
Al-Hafidz Ibn Kathir interprets that this cursed tree is an zaqqum tree. (Tafsir Ibn Kathir, 5/92).
This verse was revealed to warn the heathen when Prophet Muhammad explained about the threat of the afterlife. At that time the Prophet Muhammad 'alaihi Wassalam explains what he saw while traveling Isra' Mi'raj one of them zaqqum tree. But this makes them even more unbelievers. They wondered how a tree could grow at the bottom of a fire where the fire burned.
Allahu'alam bishawwab