Islām (Arabic: الإسلام) is among monotheistic and Abrahamic religions. The messenger of this religion was Prophet Muhammad (a) who brought the Qur'an to humanity via revelation from God. The beginning of invitation to Islam was made in 610 CE in the city of Mecca in the Arabian Peninsula. Increasing expansion of Islam began after emigration of the Prophet (s) to Medina. Muslims believe that the Prophet (a) is the last divine prophet and Islam is the last divine religion.The Qur'an and tradition of the Prophet (a) and Imams (a) is the most essential source for knowing Islamic beliefs and practices. Muslims believe that there is no falsehood or error in the Qur'an and it has remained unaltered since its revelation. Tradition includes the speeches and acts of the Prophet (a) and Imams (a) transmitted to us in written form from one generation to another.

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The most important ideological principles in Islam are monotheism, prophethood of the Prophet of Islam (a) and the hereafter. The most important practices in Islam are daily prayers, fasting, khums, zakat, hajj, and jihad. A great part of Islamic sources deal with introduction of good and bad moral issues and practical ways to acquire moral perfections. Advising about people's rights and orders for regulation of social and family relationships are among moral teachings of Islam. For many issues in daily life, Islam has orders, such as for marriage, divorce, buying and sale, mortgage and judgment, the rulings for which are discussed in the books of fiqh (jurisprudence) under the title of transactions.There are two major schools of Shi'a and Sunni in Islam, each of which has different branches. The major difference between the two is over the issue of imamate or caliphate after the Prophet (a); however, they have differences over ideological issues and rulings as well.Today, Muslims live in most countries of the world, whose population is around 1.5 billion people. Most Muslims live in Asia and especially in the Middle East.

Terminology
The word "Islam" is derived from the root s-l-m which means "being healthy and away from any defect or corruption" and has also been used to mean as "submission, total unconditional obedience, acceptance of divine ruling and sincerity in worship." Among Arabs of Arabian Peninsula before Islam, the term only had the meaning of "abandoning and giving up something" and Arabs used the verb "aslam-a" when a person gave up something very dear and precious and left it to someone else who wanted it; and if that thing is the person's own self, which is the most precious thing human possesses; then, "Islam" means "total unconditional obedience and submission." According to Seyyed Hossein Nasr, "A Muslim is he who has chosen to submit his will to divine will." According to 'Allama Tabataba'i, the reason for naming this religion as Islam is that in this religion, the servant is submitted to the will of God, the Glorified.

The word "Islam" is used in the Qur'an. According to some verses, no religion other than Islam is accepted, and after the Prophet (a) brought Islam, the only religion valid before God is Islam. Many hadiths have been transmitted from the Prophet (a) in which he (a) called his religion Islam and called his followers "Muslim".In categorization of religions, Islam is a divine, monotheistic and Abrahamic religion. Muslims believe in the One God. The Prophet of Islam (a) is Muhammad b. 'Abd Allah (a) who was sent by God to deliver divine message (or the revelation) to people. The Qur'an contains the divine revelation sent to Prophet Muhammad (a).

Difference between Islam and Faith
Anyone who says the two shahadatayn phrases, "Ashhad-u an la ilah-a illa Allah" ["I give testimony that there is no god but Allah"] and "Ashhad-u ann-a Muhammad-an rasul Allah" ["I give testimony that Muhammad (a) is the Messenger of Allah"] enters the religion of Islam. Saying these sentences is in fact giving testimony to Oneness of God and the mission of the Prophet of Islam (a); without saying which, the person is outside Islam and is considered a disbeliever.This definition of Muslim is a basic level explanation of accepting Islam. At this level, it is even possible that there would be difference between what one says and what is in his heart, because accepting Islam is a basic and apparent step in accepting the Prophet's (a) religion by saying shahadatayn, but faith requires Shahadatayn as well as heartfelt and spiritual belief. Accepting Islam includes expressing submission and obedience by the tongue and also by the limbs whether it is followed by the heart or not; but faith includes submission together with heartfelt belief.

The Prophet (a)
The founder of Islam was Prophet Muhammad b. 'Abd Allah b. 'Abd al-Muttalib (a). Based on Islamic sources, he (a) was the last messenger of God sent to humans. Muslims regard him the best of humans and the best role model for life. Many Muslims believe that Prophet Muhammad (a) was infallible and had the knowledge of the Unseen.He (a) was Arab, born in 570 CE in Quraysh tribe who lived in Mecca in Arabian Peninsula. In early childhood, he (a) lost his parents and was raised under guardianship of his grandfather 'Abd al-Muttalib and after his demise, under guardianship of his uncle Abu Talib.During his lifetime, he (a) never followed idol-worshipping which was common in Mecca. People of Mecca knew him for his trustworthiness. At the age of forty, God chose him as the Messenger (Bi'tha). The first message of God was sent to him then, by angel Gabriel in the cave of Hira in Mecca.

Divine Book
The holy divine book of Muslims is the Qur'an which is the major source of their beliefs and practices. According to Islamic beliefs, the text of the Qur'an is divine revelation sent from Allah by angel of revelation (Gabriel) to the Prophet (s). Muslims believe that there is no falsehood or error in the Qur'an and it has remained unaltered since its revelation. (See: integrity of the Qur'an) The Qur'an is a book in 114 chapters, each of which contains some verses.

Sources
The Qur'an, the tradition of the Prophet (a) and Imams of Shi'a (a) and also the speeches and acts of the Companions of the Prophet (a) are among the sources to which Muslims refer for learning about beliefs, practical duties, history of Islam and the lives of religious dignitaries. This tradition is acquired in the form of the books of hadiths and tradition from the past generations to next generations.In the view of Shi'a, only the conduct of the Prophet (a) and Imams (a) is valid for acquiring knowledge and practice. Relying on the conduct of the Companions is among characteristics of Sunni people. Shi'a regard the conduct of companions criticizable.Most important books of hadiths for Shi'a are the Four Books: al-Kafi written by al-Kulayni, Tahdhib al-ahkam and al-Istibsar written by al-Shaykh al-Tusi and Man la yahduruh al-faqih written by al-Shaykh al-Saduq.The most important books of hadiths for Sunni people are known as Sihah al-Sitta (the Six Correct Ones) which are: Sahih al-Bukhari, Sahih Muslim, Sunan al-Nasa'i, Sunan Ibn Maja, Sunan Ibn Dawud, and Sahih al-Tirmidhi.

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Principles of Religion
Ideological principles are a set of beliefs including Islam's views towards the world, human being, nature, and their relations with God. The set of Islamic beliefs is contained in the three general principles of tawhid [oneness of God], nubuwwa [prophethood] of the Prophet Muhammad (s), and ma'ad [resurrection] which are called Usul al-Din [Principles of Religion], i.e. things which every Muslim needs to believe in. Other Islamic beliefs have roots in these three beliefs. Each of these beliefs makes Islam to be distinguished from other religions. In Shi'a school, Imamate is also considered among ideological principles. Islamic beliefs are in fact the manifestation of Islamic worldview.

Oneness of God
In Islamic ideology, the most important belief is tawhid; i.e. believing in the One God. In Islamic beliefs, God is the Creator of all the existence and its Sustainer. Believing in Oneness of God is in three aspects of unity in essence, unity in attributes, and unity in actions. These three aspects in fact form theoretical tawhid and are just present in the realm of a Muslim's beliefs.Practical tawhid is the result of theoretical tawhid and is manifested in branches such as tawhid in worship, tawhid in legislation, and tawhid in domination.

Prophethood
Muslims believe that God has chosen some people as messengers to send to humans. In Islamic literature, these people are called "nabi" [prophet] and "rasul" [messenger]. The number of divine prophets is a hundred and twenty four thousand, five of whom are Ulu l-'Azm [literally: "Having Will"] and had certain duties. These prophets (a) brought religions and books. In the Qur'an, which is the last divine book, the names of twenty-six of the Prophets (a) and the books of some of them are mentioned.The last divine prophet is Prophet Muhammad (a) who brought the religion of Islam and no divine prophet will come after him. (see: khatamiyya)

Imamate
Imamate means leadership of people's affairs with regards to religion and the world in the place of the Prophet (s). In this regard, there are two major views among Muslims:Shi'a believe that the Prophet (a) announced his caliph by the order of God and people should obey him. This caliph was Ali b. Abi Talib (a) and after him, Imam al-Hasan (a) and then Imam al-Husayn (a) were Imams. Twelver Shi'a believe that after Imam al-Husayn (a), nine men of his progeny were Imam by the will of God. The Twelfth Imam was al-Mahdi (a) who is hidden from the public will come to establish justice in the world. Some sects of Shi'a such as Zaydiyya, Isma'iliyya and some others have different opinions about Imams after Imam al-Husayn (a).Sunnis believe that the Prophet (a) did not choose a caliph after himself; thus, after his demise, people chose [[Abu Bakr b. Abi Quhafa] and gave allegiance to him. After him, they regarded 'Umar b. al-Khattab and then 'Uthman b. 'Affan the second and third caliphs and considered 'Ali b. Abi Talib (a) the fourth caliph.

Resurrection
Believing in resurrection of the dead and the life after death is among the principles of beliefs among religions, especially Islam. Believing in the hereafter includes the belief in the events at the time of death and after it during the time in barzakh and also the event and situation after revival on the Day of Resurrection. Concepts such as resurrection, balance, tatayur al-kutub (distributing everyone's book [of actions]) and passing sirat bridge are among the issues Muslims believe.

Other Beliefs
Believing in angels, decree and destiny, the world of dhar, creation of Prophet Adam (a) from soil and the lineage of human from him and Eve are among the beliefs of all or most Muslims.