Praise be to Allah.
Iblis – may Allah curse him – is one of the jinn. He was not an angel for a single day, not even for an instant. The angels were created noble; they never disobey Allah when He commands them to do something and they do what they are commanded. This is clearly stated in the Quranic texts which indicate that Iblis is one of the jinn and not one of the angels. These texts include the following:
1. Allah says (interpretation of the meaning):
“And (remember) when We said to the angels: “Prostrate yourselves unto Adam.” So they prostrated themselves except Iblis (Satan). He was one of the jinn; he disobeyed the command of his Lord. Will you then take him (Iblis) and his offspring as protectors and helpers rather than Me while they are enemies to you? What an evil is the exchange for the Zalimoon (polytheists, and wrongdoers, etc).” [18:50]
2. Allah stated that He created the jinn from fire, as He says (interpretation of the meaning):
“And the jinn, We created aforetime from the smokeless flame of fire” [15:27]
“And the jinn He created from a smokeless flame of fire” [55:15]
And it was narrated in a saheeh hadeeth (authentic report) that ‘Aishah (may Allah be pleased with her) said: the Messenger of Allah (peace and blessings of Allah be upon him) said: “The angels were created from light, the jinn were created from smokeless fire and Adam was created from that which has been described to you.” [Muslim, Ahmad, al-Bayhaqi and Ibn Hibban].
One of the attributes of the angels is that they were created from light, and the jinn were created from fire. It was mentioned in the Quran that Iblis – may Allah curse him – was created from fire. This is what Iblis himself said when Allah, may He be glorified and exalted, asked him the reason for his refusal to prostrate to Adam when Allah commanded him to do so. He – may Allah curse him – said:
“ ‘I am better than him (Adam), You created me from fire, and him You created from clay.’” [7:12, 38:76 – interpretation of the meaning]. This indicates that he was one of the jinn.
3. Allah has described the angels in His Book, where He says (interpretation of the meaning):
“O you who believe! Ward off yourselves and your families against a Fire (Hell) whose fuel is men and stones, over which are (appointed) angels stern (and) severe, who disobey not, (from executing) the commands they receive from Allah, but do that which they are commanded.” [66:6]
“And they say: ‘The Most Gracious (Allah) has begotten a son (or children).’ Glory to Him! They [whom they call children of Allah i.e. the angels, ‘Isa (Jesus) son of Maryam, ‘Uzair (Ezra)], are but honoured slaves. They speak not until He has spoken, and they act on His command.” [21:26-27]
“And to Allah prostrate all that is in the heavens and all that is in the earth, of the moving (living) creatures and the angels, and they are not proud [i.e. they worship their Lord (Allah) with humility]. They fear their Lord above them, and they do what they are commanded.” [16:49-50]
So it is not possible for the angels to disobey their Lord, because they are protected from sin and they are naturally inclined to obey Allah.
4. The fact that Iblis is not one of the angels means that he is not compelled to obey Allah. He has freedom of will just as we humans do. Allah says (interpretation of the meaning):
“Verily, We showed him the way, whether he be grateful or ungrateful.” [76:3]
There are also Muslims and kafirs (non-Muslims) among the jinn. It says in Soorat al-Jinn (interpretation of the meaning):
“Say (O Muhammad): ‘It has been revealed to me that a group (from three to ten in number) of jinn listened (to this Quran). They said: ‘Verily, we have heard a wonderful Recitation (this Quran)! It guides to the right path, and we have believed therein, and we shall never join (in worship) anything with our Lord (Allah).’” [72:1-2]
In the same soorah (chapter), it states that the jinn said:
“‘And indeed when we heard the Guidance (this Quran), we believed therein (Islamic Monotheism), and whosoever believes in his Lord shall have no fear, either of a decrease in the reward of his good deeds or an increase in the punishment for his sins. And of us some are Muslims (who have submitted to Allah, after listening to this Quran), and of us some are Al‑Qasitoon (disbelievers those who have deviated from the right path)…” [72:13-14]
Ibn Kathir (may Allah have mercy on him) said in his exegesis:
Al-Hasan al-Basri said: Iblis was not one of the angels, not even for a single moment. He is the father of the jinn, just as Adam (peace be upon him) is the father of mankind. This was narrated by al-Tabari with a saheeh isnad (authentic chain).
Some of the scholars said that Iblis was one of the angels, that he was the peacock of the angels, that he was the one among the angels who strove the hardest in worship … and other reports, most of which come from the Israiliyyat (stories and reports from Jewish sources), and some of which contradict the clear texts of the Quran.
Ibn Kathir said, explaining this:
A lot of these reports were transmitted from the salaf (pious predecessors), and most of them come from the Israiliyyat, which may have been transmitted in order to be examined [i.e., as opposed to being accepted as is]. Allah knows best about the veracity or otherwise of many of them. Some of them are definitely to be rejected, because they go against the truth which we hold in our hands. In the Quran we have what is sufficient so that we have no need for previous reports, because hardly any of them are free of distortions, with things added or taken away. Many things have been fabricated in them, for they did not have people who had memorized things precisely by heart (huffaz) who could eliminate the distortions created by extremists and fabricators, unlike this ummah (nation) which has its imams (religious leaders), scholars, masters, pious and righteous people, brilliant critics and men of excellent memory who recorded the hadeeths (reports) and classified them, stating whether they were saheeh (sound), hasan (good), da’eef (weak), mawdoo’ (fabricated) or matrook (to be ignored). They identified the fabricators and liars, and those about whom nothing was known, and other kinds of men (i.e., narrators). All of this afforded protection to the Prophet (peace and blessings of Allah be upon him), the seal of the Messengers and the leader of Mankind, so that nothing would be attributed to him falsely and nothing would be transmitted from him that he did not say or do. May Allah be pleased with them and make them pleased [by rewarding them], and make the Paradise of al-Firdaws their eternal abode. (Tafseer al-Quran il-‘Azeem).
And Allah knows best.