In Islam, the meaning of "Tawhid" is the oneness of Allah, or God. This concept appears in the Shah?dah, the verbal formula central to Islam that states, "There is no god but God, and Muhammad is his prophet."
The Shah?dah is the first of the Five Pillars of Islam. Tawhid also asserts that God is not made of parts but is one substance and entity. Because of God's essential unity, worshipping other entities is a grave sin in Islam. The Sufi branch of Islam has another conception of Tawhid, however. Sufis believe that Tawhid asserts the essential oneness of existence: outside of God, there is no existence, and therefore all things that exist partake in the essential unity of God.