Praise be to Allah.

Firstly: 

With regard to Iblees entering Hell to abide therein forever, this is something concerning which there is no doubt. Allaah has mentioned his ultimate fate in a number of verses, such as the following. 

1 – Allaah says (interpretation of the meaning): 

“(Allaah) said: ‘What prevented you (O Iblees) that you did not prostrate yourself, when I commanded you?’ Iblees said: ‘I am better than him (Adam), You created me from fire, and him You created from clay.’

13. (Allaah) said: ‘(O Iblees) get down from this (Paradise), it is not for you to be arrogant here. Get out, for you are of those humiliated and disgraced.’

14. (Iblees) said: ‘Allow me respite till the Day they are raised up (i.e. the Day of Resurrection).’

15. (Allaah) said: ‘You are of those respited.’

16. (Iblees) said: ‘Because You have sent me astray, surely, I will sit in wait against them (human beings) on Your straight path.

17. ‘Then I will come to them from before them and behind them, from their right and from their left, and You will not find most of them as thankful ones (i.e. they will not be dutiful to You).’

18. (Allaah) said (to Iblees): ‘Get out from this (Paradise), disgraced and expelled. Whoever of them (mankind) will follow you, then surely, I will fill Hell with you all’”

[al-A’raaf 7:12-18]

Al-Tabari said: 

This is an oath from Allaah, may He be glorified and exalted; He swore that whoever among the sons of Adam followed the enemy of Allaah Iblees and obeyed him, He would fill Hell with them all, i.e., with the disbelievers among the sons of Adam who followed Iblees, and with Iblees and his offspring. End quote. 

Tafseer al-Tabari, 8/139 

2 – Allaah says (interpretation of the meaning): 

“(Allaah) said: ‘O Iblees (Satan)! What is your reason for not being among the prostrators?’

33. [Iblees (Satan)] said: ‘I am not the one to prostrate myself to a human being, whom You created from dried (sounding) clay of altered mud.’

34. (Allaah) said: ‘Then, get out from here, for verily, you are Rajeem (an outcast or a cursed one).

35. ‘And verily, the curse shall be upon you till the Day of Recompense (i.e. the Day of Resurrection).’

36. [Iblees (Satan)] said: ‘O my Lord! Give me then respite till the Day they (the dead) will be resurrected.’

37. Allaah said: ‘Then verily, you are of those reprieved,

38. ‘Till the Day of the time appointed.’

39. [Iblees (Satan)] said: ‘O my Lord! Because You misled me, I shall indeed adorn the path of error for them (mankind) on the earth, and I shall mislead them all.

40. ‘Except Your chosen, (guided) slaves among them.’

41. (Allaah) said: ‘This is the Way which will lead straight to Me.’

42. ‘Certainly, you shall have no authority over My slaves, except those who follow you of the Ghaawoon (Mushrikoon and those who go astray, criminals, polytheists, and evildoers).

43. ‘And surely, Hell is the promised place for them all.

44. ‘It (Hell) has seven gates, for each of those gates is a (special) class (of sinners) assigned’”

[al-Hijr 15:32-44]

 Al-Shanqeeti (may Allaah have mercy on him) said:  

Every verse which mentions how Iblees misguides the sons of Adam also states that Iblees and all those who follow him will be in Hell, as Allaah says here: “And surely, Hell is the promised place for them all. It (Hell) has seven gates ”. 

Adwa’ al-Bayaan, 3/131 

3 – And Allaah said:

“(Allaah) said: The truth is — and the truth I say

85. That I will fill Hell with you [Iblees (Satan)] and those of them (mankind) that follow you, together”

[Saad 38:84, 85]

4 – Allaah tells us that the jinn said (interpretation of the meaning): 

“And of us some are Muslims (who have submitted to Allaah, after listening to this Qur’aan), and of us some are Al‑Qaasitoon (disbelievers those who have deviated from the Right Path). And whosoever has embraced Islam (i.e. has become a Muslim by submitting to Allaah), then such have sought the Right Path.

15. And as for the Qaasitoon (disbelievers who deviated from the Right Path), they shall be firewood for Hell”

[al-Jinn 72:14, 15]

Secondly: 

With regard to how Iblees will be punished with fire when he is created from fire, the answer is: 

The fact that the jinn were created from fire does not necessarily mean that they are fire now, just as man was created from dust but he is not dust now. 

Abu’l-Wafa’ ibn Aqeel said: 

The devils and jinn are attributed to fire just as man is attributed to dust, clay and baked clay. What is meant in the case of man is that he originates from clay, but a human being is not clay in a real sense, rather he used to be clay. Similarly the jinn were fire in the beginning. End quote. 

Laqt al-Marjaan fi Ahkaam al-Jaan, p. 33, quoted in ‘Aalim al-Jinn wa’l-Shayaateen, p. 58. 

Although man was created from clay, a little of it will harm him; if he is buried beneath it he will die, and if he is struck with it (such as with baked clay), he will be wounded or will die. So it not strange to think that although the jinn were created from fire, they will be punished with the Fire of Hell. 

Allaah created the jinn from fire, but they are not fire now. There is a great deal of evidence to that effect, such as the following: 

1 – It was narrated from ‘Aa’ishah that the Messenger of Allaah (peace and blessings of Allaah be upon him) was praying, then the Shaytaan came to him and he seized him, threw him to the ground and strangled him. The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Until I felt the coolness of his tongue on my hand. Were it not for the prayer of my brother Sulaymaan, he would have been tied up this morning so that the people could see him.” Narrated by al-Nasaa’i in al-Sunan al-Kubra, 6/442; classed as saheeh by Ibn Hibbaan, 6/115 

2 – It was narrated that Abu’l-Darda’ said: The Messenger of Allaah (peace and blessings of Allaah be upon him) stood (in prayer) and we heard him say: “I seek refuge with Allaah from you.” Then he said: “I curse you with the curse of Allaah,” three times, and he reached out his hand as if to take something. When he had finished praying, we said: “O Messenger of Allaah, we heard you say something in your prayer that we have never heard you say before, and we saw you reaching out your hand.” He said: “The enemy of Allaah Iblees came with a brand of fire to throw it in my face, so I said, ‘I seek refuge with Allaah from you,’ three times, then I said: ‘I curse you with the full curse of Allaah,’ but he did not go back, three times. Then I wanted to seize him, and by Allaah, were it not for the prayer of our brother Sulaymaan, this morning he would have been tied up and the children of the people of Madeenah would have played with him.” Narrated by Muslim, 542. 

From these two hadeeths it is clear to us that the jinn are not fire now. This is indicated by the coolness that the Messenger of Allaah (peace and blessings of Allaah be upon him) felt from the tongue of the Shaytaan, as stated in the first hadeeth. If the Shaytaan was still in the form of fire, he would not have needed to bring a brand of fire to throw in the face of the Prophet (peace and blessings of Allaah be upon him), and the children would not have been able to play with him. 

3 – The Prophet (peace and blessings of Allaah be upon him) said: “The Shaytaan flows through the son of Adam as blood flows.” Narrated by al-Bukhaari (1933) and Muslim (2175). 

If the Shaytaan was fire, he would burn man, because the Shaytaan is inside him. So we can see the difference between the Shaytaan being fire and being created from fire. 

If the Shaytaan were fire now – for the sake of argument – and Allaah wanted to punish him with the Fire of Hell, then Allaah is Able to do all things, and He is not incapable of anything, may He be glorified and exalted. 

And Allaah knows best.