Shahada in the context of "Saudi Arabian flag"

Islam is an Abrahamic monotheistic religion based on the Quran and the teachings of Muhammad. Adherents of Islam are called Muslims, who are estimated to number 2 billion worldwide and are the world's second-largest religious population, after Christianity.

Muslims believe that there is a primordial faith that was revealed many times through earlier prophets and messengers, including Adam, Noah, Abraham, Moses, and Jesus, and they believe that Islam is the universal and complete version of this faith. Muslims consider the Quran to be the verbatim word of God and the unaltered, final revelation. Alongside the Quran, Muslims also believe in previous revelations, such as the Tawrat (the Torah), the Zabur (Psalms), and the Injil (Gospel). They believe that Muhammad is the main and final of God's prophets, through whom the religion was completed. The teachings and normative examples of Muhammad, called the Sunnah, documented in accounts called the hadith, provide a constitutional model for Muslims. Islam is based on the belief in the oneness and uniqueness of God (tawhid), and belief in an afterlife (akhirah) with the Last Judgment—wherein the righteous will be rewarded in paradise (jannah) and the unrighteous will be punished in hell (jahannam). The Five Pillars, considered obligatory acts of worship, are the Islamic oath and creed (shahada), daily prayers (salah), almsgiving (zakat), fasting (sawm) in the month of Ramadan, and a pilgrimage (hajj) to Mecca. Islamic law, sharia, touches on virtually every aspect of life, from banking and finance and welfare to men's and women's roles and the environment. The two main religious festivals are Eid al-Fitr and Eid al-Adha. The three holiest sites in Islam are Masjid al-Haram in Mecca, Prophet's Mosque in Medina, and al-Aqsa Mosque in Jerusalem.

Tawhid, literally "to unite" or "to make one", refers to the principle of monotheism in Islam. It is the religion's central and single most important concept, upon which a Muslim's entire religious adherence rests. It unequivocally holds that God is indivisibly one (ahad) and single (wahid).

Tawhid constitutes the foremost article of the Muslim profession of submission. The first part of the Islamic declaration of faith (shahada) is the declaration of belief in the oneness of God. To attribute divinity to anything or anyone else, is considered shirk, which is an unpardonable sin unless repented afterwards, according to the Qur'an. Muslims believe that the entirety of the Islamic teaching rests on the principle of tawhid.

The Five Pillars of Islam (arkān al-Islām أركان الإسلام; also arkān ad-dīn أركان الدين "pillars of the religion") are fundamental practices in Islam, particularly Sunni Islam, considered to be obligatory acts of worship for all Muslims. They are summarized in the hadith of Gabriel. The Sunni and Shia agree on the basic details of the performance and practice of these acts, but Shia denominations may have their own lists of pillars that differ from the Sunni five, such as the Twelver Ancillaries of the Faith (consisting of four pillars and six obligatory acts) and the Ismaili Seven Pillars. The five pillars are: profession of faith (Shahada), prayer (Salah), almsgiving (Zakat), fasting in the month of Ramadan (Sawm), and pilgrimage to Mecca (Hajj).

Salah (Arabic: ٱلصَّلَاةُ, romanized: aṣ-Ṣalāh, also spelled Salat), also known as Namaz (Persian: نماز, romanized: namāz), is the practice of formal worship in Islam, consisting of a series of ritual prayers performed at prescribed times daily. These prayers, which consist of units known as rak'ah, include a specific set of physical postures, recitation from the Quran, and prayers from the Sunnah, and are performed while facing the direction towards the Kaaba in Mecca (qibla). The number of rak'ah varies depending on the specific prayer. Variations in practice are observed among adherents of different madhahib (schools of Islamic jurisprudence). The term salah may denote worship in general or specifically refer to the obligatory prayers performed by Muslims five times daily, or, in some traditions, three times daily.

The obligatory prayers play an integral role in the Islamic faith, and are regarded as the second and most important, after shahadah, of the Five Pillars of Islam for Sunnis, and one of the Ancillaries of the Faith for Shiites. In addition, supererogatory salah, such as Sunnah prayer and Nafl prayer, may be performed at any time, subject to certain restrictions. Wudu, an act of ritual purification, is required prior to performing salah. Prayers may be conducted individually or in congregation, with certain prayers, such as the Friday and Eid prayers, requiring a collective setting and a khutbah (sermon). Some concessions are made for Muslims who are physically unable to perform the salah in its original form, or are travelling.

Conversion to Islam, also known within Islam as reversion, is adopting Islam as a religion or faith. Conversion requires a formal statement of the shahādah, the credo of Islam, whereby the prospective convert must state that "there is none worthy of worship in truth except Allah and Muhammad is the messenger of Allah". Proselytism of the faith is referred to as "dawah", and missionary efforts have been promoted since the dawn of the religion in the 7th century.