thumb|upright=0.8|Muslims use the single raised index finger gesture (al-sabbaba or al-sabbaha) as a symbol of tawhid.
Tawhid, literally "Oneness" or "to make one", refers to the principle of monotheism in Islam, which is the single most important and central concept, upon which a Muslim's entire religious adherence rests. It unequivocally holds that God (Allāh) 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. Muslims believe that the entirety of the Islamic teaching rests on the principle of tawhid.
From an Islamic standpoint, there is an uncompromising nondualism at the heart of the Islamic beliefs (aqida) that is seen as distinguishing Islam from other major religions.
The Quran teaches the existence of a single and absolute truth that transcends the world, a unique, independent and indivisible being that is independent of all of creation. God, according to Islam, is a universal God, rather than a local, tribal or parochial one and is an absolute that integrates all affirmative values.
Islamic intellectual history can be understood as a gradual unfolding of the manner in which successive generations of believers have understood the meaning and implications of professing tawhid. Islamic scholars have different approaches toward understanding it. Islamic scholastic theology, jurisprudence, philosophy, Sufism, and even the Islamic understanding of natural sciences to some degree, all seek to explain at some level the principle of tawhid.
Chapter 112 of the Quran, titled al-Ikhlas, reads:
Etymology
The word <nowiki/>'tawhid'<nowiki/> (), which means "He asserted, or declared, God to be one", is derived from the Arabic root wahhada<nowiki/>' (), which means "to unite" or "to make one". This term signifies the belief in absolute oneness and uniqueness of God. This reflects the struggle of monotheism against polytheism.
Name of God in Islam
In order to explain the complexity of the unity of God and of the divine nature, the Quran uses 99 terms, which are referred to as "Excellent Names of God" (). The divine names project divine attributes, which in turn project all the levels of the creation down to the physical plane. Aside from the supreme name "Allah" and the neologism ar-Rahman (referring to the divine beneficence that creates and maintains the universe) and a few other specific names like Malik al-Muluk ("King of Kings") in an authentic narration of Muhammad, other names may be shared by both God and human beings. According to Islamic teachings, the latter is meant to serve as a reminder of God's immanence, rather than being a sign of one's divinity or, alternatively, imposing a limitation on God's transcendent nature. Attribution of divinity to a created entity, shirk, is considered a denial of the truth of God and thus is a major sin. Alternatively, the translation 'associating [with God]' has been suggested. The term includes denial of attributing any form of divinity to any other thing but God, which includes the self by elevating oneself above others That has caused Sunni scholars to accuse Salafis and Wahhabis of depicting God as a created object ruling from the sky.
Shirk is classified into two categories:
- al-Shirk al-akbar (; ): open and apparent
- al-shirk al-khafi; ): concealed or hidden. It is when people perform the necessary rituals but not for God but for the sake of others, including social recognition. Hidden shirk might be unwitting, yet punishable, although to a lesser extent than greater forms of shirk.
Vincent J. Cornell, a scholar of Islamic studies quotes the following statement from Ali: