Tawḥīd

Tawhid (Arabic: توحيد‎‎ tawḥīd, meaning the oneness [of God]"; also transliterated as Tawheed and Touheed) is the indivisible oneness concept of monotheism in Islam. Tawhid is the religion's most fundamental concept and holds that God (Allah, literally Al-Ilāh "the God") is One (Al-ʾAḥad) and Single (Al-Wāḥid). Because of the "principle of Tawhid the Islamic belief in God is considered Unitarian."

Tawhid constitutes the foremost article of the Muslim profession of faith. The first part of the Shahada (the Islamic declaration of faith) is the declaration of belief in the oneness of God. To attribute divinity to a created entity, known as shirk, is an unpardonable sin according to the Qur'an. Muslims believe that the entirety of the Islamic teaching rests on the principle of Tawhid.

There is an uncompromising monotheism at the heart of the Islamic beliefs (Aqidah) which is seen, from an Islamic standpoint, as distinguishing Islam from other major religions. However, Tawhid is analogous to the monotheistic concept of God in Judaism as declared in the Shema (the Jewish declaration of faith), and is also analogous to Christian Unitarianism adhered to by a minority of Christian denominations affirming the oneness and indivisibility of God in Christianity (in contrast to the "One God in Three Persons" Trinity of most Christian faiths).

...
Wikipedia