Iblees was not one of the angels

My friend told me that iblis (shaitan) used to be an angel. My wife
says that this is not true. Could you please give me some information.
Praise be to Allaah.
Iblees was definitely not one of the angels. This is indicated by
three things: the clear texts of the Qur'aan, the physicalattributes
of Iblees and the attitude of Iblees.
1 – With regard to the clear statements of the Qur'aan, Allaah says
(interpretation of the meaning):
"And (remember) when We said to the angels: 'Prostrate yourselves unto
Adam.' So they prostrated themselves except Iblees (Satan). He was one
of the jinn"
[al-Kahf 18:50]
Al-Hasan al-Basri said: Iblees was never one of the angels, not even
for an instant. 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 isnaad as stated by Ibn
Katheer in his Tafseer, 3/89.
2 – With regard to his physical attributes, Allaah stated that He
created him from fire. Allaah says (interpretation of the meaning):
"He created man (Adam) from sounding clay like the clay of pottery.
And the jinn He created from a smokeless flame of fire"
[al-Rahmaan 55:14, 15]
and it was narrated in Saheeh Muslim (2996) from the hadeeth of
'Aa'ishah (may Allaah be pleased with her) that the Prophet (peace and
blessings of Allaah be upon him) said: "The angels were created from
light, the jinn werecreated from smokeless fire, and Adam was created
from that which has been described to you."
So it is clear that there is a difference between the physical nature
of the angels and that of Iblees, and he is definitely not one of
them.
3 – With regard to his attitude, Iblees disobeyed Allaah by not
prostrating to Adam, butwe know from the Qur'aan that it is impossible
for the angelsto disobey Allaah. Allaah says (interpretation of the
meaning):
"…angels stern (and) severe, who disobey not,(from executing) the
Commands they receive from Allaah, but do that which they are
commanded"
[al-Tahreem 66:6]
Some reports which are not saheeh have been narrated from some of the
salaf, suggesting that Iblees was the best of the angels, that he was
one of the keepers of Paradise, etc. Imaam Ibn Katheer commented on
that by saying:
Many reports to that effect have been narrated from the salaf, but
most of them come from the Isra'eeliyyaat (reports narrated from
Jewish sources) which were narrated to be examined. Allaah knows best
about the true status of many of them. There are some which can be
rejected out of hand because they go against the truth that wehave
before us. In the Qur'aan there is sufficient information that we have
no need of earlier reports, because hardly any of them are free from
alterations, additions and subtractions, and many things have been
fabricated in them. The earlier nations did not have scholars to
examine these reports and eliminate those which are not sound, as
this ummah has its imams and scholars who have great knowledge and are
pious and righteous, who wrote down the hadeeth and examined it and
showedwhat is sound and what is not, and what is fabricated,
identifying the fabricators, liars and those narrators who were
unknown, and other categories of narrators. All of that was to protect
the status of the Prophet, the Seal of the Prophets and the leader of
mankind (peace and blessings of Allaah be upon him), lestany lie be
attributed to him and lest anything beattributed to him that hedid not
say or do. May Allaah be pleased with them and make them please and
make the Paradise of al-Firdaws their abode.
Tafseer al-Qur'aan il-'Azeem, 3/90.