Islaam is the Deen which Allaah has sent Muhammad (sal-Allaahu ‘alayhe wa-sallam) with; Allaah made it the last of religions and perfected it for His creation; He made it a completion of His Favours upon them, and chose it to be their Deen; No other religion is accepted from anyone except the Deen of Islaam. Allaah, Ta’aalaa, says:
“Muhammad (sal-Allaahu ‘alayhe wa-sallam) is not the father of any man among you, but he is the Messenger of Allaah, and the Last (end) of the Prophets.” [Qur’aan 33:40]
He also says:
“This day , I have perfected your religion for you, and completed my Favour upon you, and have chosen for you Al-Islaam as your Deen.” [Qur’aan 5:3]
“Truly, the Deen before Allaah is Al-Islaam.”  [Qur’aan 3:19]
“And whosoever seeks a religion other than Islaam, it will never be accepted of him, and in the Hereafter he will be one of the losers.” [Qur’aan 3:85]
Allaah Ta’aalaa ordained that mankind must submit to Him in Islaam. He said addressing His Messenger (Muhammad sal-Allaahu ‘alayhe wa-sallam):
“Say (O Muhammad sal-Allaahu ‘alayhe wa-sallam) ‘O mankind! Verily, I am sent to you all as the Messenger of Allaah - to whom belongs the dominion of the heavens and the earth. La ilaaha illa Huwa (none has the right to be worshipped but He); it is He who gives life and causes death. So believe in Allaah and His Messenger (Muhammad sal-Allaahu ‘alayhe wa-sallam), the Prophet who can neither read nor write, who believes in Allaah and His Words , and follow him so that you may be guided.” [Qur’aan 7:158]
It is reported in Saheeh Muslim  on the authority of Abu Hurairah (radhi-Allaahu ‘anhu ), that Allaah’s Messenger (sal-Allaahu ‘alayhe wa-sallam) said:
“By Him (Allaah) in Whose Hand Muhammad’s soul is, there is none from amongst the Jews and the Christians (of these present nations) who hears about me and then dies without believing in the Message with which I have been sent (i.e. Tawheed), but he will be from the dwellers of the (Hell) Fire.” 
The belief in the Prophet Muhammad (sal-Allaahu ‘alayhe wa-sallam) is the attestation with full acceptance and submission, not just mere attestation, that what he brought forth is the truth. That is why Abu Taalib (the uncle of the Prophet sal-Allaahu ‘alayhe wa-sallam) did not become a believer in the Messenger (sal-Allaahu ‘alayhe wa-sallam), despite his attestation to what the Prophet (sal-Allaahu ‘alayhe wa-sallam) brought forth and his witness that it is the best of religions.
The Deen of Islaam embraces all of the human welfare that is comprised in the previous religions; it is distinguished above all religions in its suitability for all times, places, and nations. Allaah (Ta’aalaa) addresses His Messenger (sal-Allaahu ‘alayhe wa-sallam) saying:
“And We have sent down to you (O Muhammad sal-Allaahu ‘alayhe wa-sallam) the Book (this Qur’aan) in truth, confirming the Scripture that came before it and Muhayminan (trustworthy in highness and a witness) over it (old Scripture).” [Qur’aan 5:48]
The suitability of the Deen means that adhering to Islaam does not contradict the welfare of the Ummah (Muslim community at large) in any place or in any time. Indeed it is its betterment. This does not mean, however, that the Deen is subjugate to every time, place, and Ummah as some people like it to be.
The Deen of Islaam is the Deen of the Truth, whoever truly adheres to it, Allaah guarantees him victory and makes him prevail on everyone else who doesn’t. Allaah (Ta’aalaa) says:
“He it is Who sent His Messenger (Muhammad sal-Allaahu ‘alayhe wa-sallam) with guidance and the Deen of the truth to make it prevail over all (other) religions even though the Mushrikeen hate (it).” [Qur’aan 61:9]
“Allaah has promised, to those among you who believe, and do righteous deeds, that He will certainly grant them succession to (the present rulers) in the land, as He granted it to those before them; and that He will grant them the authority to practice their religion, that which He has chosen for them (i.e. Islaam). And He will surely give them in exchange a safe security after their fear (provided) they (believers) worship Me and do not associate anything (in worship) with Me. But whoever disbelieved after this, they are the Fasiqoun (rebellious, disobedient to Allaah).” [Qur’aan 24:55]
The Deen of Islaam is ‘Aqeedah (Creed) and Sharee’ah (Legislation), and it is perfect in both. Islaam commands:
- The Tawheed and forbids Shirk (setting associates with Allaah).
- Truthfulness, and forbids lying.
- Justice , and forbids oppression.
- Trustworthiness, and forbids treachery.
- Faithfulness, and forbids betrayal.
- To be good and dutiful to one’s parents, and forbids being disrespectful to them.
- Keep ties with relatives of kinship, and forbids severing the ties with them.
- To have good relations with one’s neighbourhood, and forbids all forms of ill-treatment to the neighbours.
Generally speaking, Islaam commands all noble morals, and forbids all ill and despicable manners; it also commands righteousness and forbids wrong. Allaah (Ta’aalaa) says:
“Verily, Allaah enjoins Al-‘Adl (i.e. justice and worshipping none but Allaah) and ‘Al-Ihsaan[/b] , and giving help to kith and kin , and forbids Al-Fahshaa’ , Al-Mankar , and Al-Baghy.”  [Qur’aan 16:90]
 This Aayah (verse) was sent down during the Hajjatul Wadaa’ (Farewell Pilgrimage) of the Prophet (sal-Allaahu ‘alayhe wa-sallam), on the Day of ‘Arafah which was a Friday. [TN]
 Which means that Islaam is the only Deen that Allaah will accept from His slaves. See the Tafseer of Ibn Katheer for the above Aayah. [TN]
 Allaah’s Words include all the Messages sent to the Prophets: The Qur’aan, the Torah, the Gospel (in their original texts), Az-Zaboor, and the Psalms. Also it includes, Allaah’s Word Kunn (Be!) - and he was i.e. Jesus, son of Mary, peace be upon him. See M. M. Khaan and M. T. al-Hilaalee's Interpretation of the Meanings of the Noble Qur'aan, Soorah 7, Aayah 158. [TN]
Is a collection of authentic hadeeth narrations compiled by Imaam Muslim: Abul Hasain Muslim ibn al-Hajjaaj ibn Muslim al Qushairi an-Naisaburi (202 (6)-261 AH / 817 (821)-875 CE). [TN]
 Radhi-Allaahu ‘Anhu (‘Anhaa, ‘Anhumaa, or ‘Anhum), may Allaah be pleased with him (her, both or them), respectively. [TN]
 Saheeh Muslim, V. 1, Hadeeth no. 284
 Justice is establishing equality between similar things and differentiating between different things. Justice is not absolute equality as generalised by some people when they say: “The Deen of Islaam is the Deen of equality” Establishing equality between different things is injustice that is not brought forth by Islaam, and the person who does that is not to be praised - a footnote by the author Shaykh Muhammad bin Saalih Al-Uthaymeen.
 Al-Ihsaan: In this Aayah it means to be patient in performing one’s duties to Allaah, totally for Allaah’s sake and in accordance with the Sunnah of the Prophet (sal-Allaahu ‘alayhe wa-sallam) in a perfect manner. [TN]
 Degree of kinship: First of all, your parents, then your offspring, then your brothers and sisters, then your paternal uncles and aunts (from the father’s side), then your maternal uncles and aunts (from your mother’s side), and then other relatives. [TN]
 Al-Fahshaa’: All evil deeds, e.g. illegal sexual intercourse, disobedience to parents, to tell lies, to steal, etc. [TN]
 Al-Munkar: All that is prohibited by Islaamic Law: polytheism, disbelief, and every kind of evil deed, etc. [TN]
 Al-Baghy: All kinds of oppression. [TN]