It is Pure Islamic Monotheism (Worshipping Allah Alone and nothing else); the religion of Ibrahim [Abraham] (Peace be upon him). Allah, Most High says: {Truly, the religion with Allah is Islam}. (Al' Imran, 19)
He says: {Do they seek other than the religion of Allah (the true Islamic Monotheism worshipping none but Allah Alone), while to Him submitted all creatures in the heavens and the earth, willingly or unwillingly}. (Al' Imran, 83)
He says: {And who turns away from the religion of Ibrahim (Abraham) (i.e. Islamic Monotheism) except him who befools himself?}. (Al-Baqarah, 130)
He says: {And whoever seeks a religion other than Islam, it will never be accepted of him, and in the Hereafter he will be one of the losers}. (Al 'Imran, 85)
He says: {Or have they partners with Allah (false gods) who have instituted for them a religion which Allah has not ordained?}. (Ash-Shura, 21)
It is to decisively admit and confess their existence and that they are from among the subjugated and worshipping creatures of Allah the Almighty. And that they are: {They (the angels) are but honored slaves. They speak not until He has spoken, and they act on His Command}. (Al-Anbiya', 26, 27)
Allah the Almighty says: {Who disobey not, (from executing) the Commands they receive from Allah, but do that which they are commanded} .(At- Tahrim, 6)
Allah the Almighty says: {And those who are near Him (i.e. the angels) are not too proud to worship Him, nor are they weary (of His worship). They (i.e. the angels) glorify His Praises night and day, (and) they never slacken (to do so)}. (Al-Anbiya', 19, 20)
Almighty Allah says regarding this, {And We have sent down to you (O Muhammad (Peace be upon him)) the Book (this Qur'an) in truth, confirming the Scripture that came before it and Muhaymin (trustworthy in highness and a witness) over it (old Scriptures)}. (Al-Ma'idah, 48)
Allah the Almighty says: {And this Qur'an is not such as could ever be produced by other than Allah (Lord of the heavens and the earth) but it is a confirmation of (the revelation) which was before it [i.e. the Taurat (Torah), and the Injeel (Gospel)], and a full explanation of the Book (i.e. laws, decreed for mankind) - wherein there is no doubt from the Lord of the `Alamin (mankind, jinn, and all that exists)}. (Yunus, 37)
Allah the Almighty says: {It (the Qur'an) is not a forged statement but a confirmation of (Allah's existing Books) which were before it [i.e. the Taurat (Torah), the Injeel (Gospel) and other Scriptures of Allah] and a detailed explanation of everything and a guide and a Mercy for the people who believe}. (Yusuf, 111)
Scholars of Exegesis say: Muhaimin means trustworthy in highness and a witness s over the old Scriptures testifying the truth that is therein and falsifying the falsehood that is added therein. Thus, all sincere adherents of the earlier Scriptures must submit and subjugate themselves to it (the Glorious Qur'an).
Allah the Almighty says:
{Those to whom We gave the Scripture [i.e. the Taurat (Torah) and the Injeel (Gospel)] before it, they believe in it (the Qur'an). And when it is recited to them, they say: "We believe in it. Verily, it is the truth from our Lord. Indeed even before it we have been from those who submit themselves to Allah in Islam as Muslims (like' Abdullah Ibn Salam and Salman Al-Farisi, etc)}, (Al-Qasas, 52, 53)