Tawhid is the assertion of the absolute oneness and uniqueness of God, and it is the foundation on which everything else in Islam rests. Its charter text is the short Surah al-Ikhlas (Qur'an 112): "Say: He is God, One; God, the Eternal Refuge; He neither begets nor is born, and there is none comparable to him." The first half of the confession of faith, "there is no god but God", is tawhid stated as a creed. Its opposite is shirk, the association of any partner with God, which the Qur'an names as the one sin God does not forgive in those who die unrepentant of it.
Later theology analysed tawhid into aspects: the oneness of God's lordship (that he alone creates and sustains), the oneness of his worship (that he alone may be worshipped), and the oneness of his names and attributes (that his qualities are his own and unlike any creature's). Much of Islamic devotion, law and art can be read as the working-out of this single insistence, that God is one, without partner, without image, and without likeness.