(“making one,” “asserting oneness”), in Islām, the oneness of God, in the sense that he is one and there is no god but he, as stated in the shahādah (“witness”) formula: “There is no god but God and Muḥammad is His prophet.” Tawhid further refers to the nature of that God—that he is a unity, not composed, not made up of parts, but simple and uncompounded. The doctrine of the unity of God and the issues that it raises, such as the question of the relation between the essence and the attributes of God, reappear throughout most of Islāmic history. In the terminology of Muslim mystics (Ṣūfīs), however, tawhid has a pantheistic sense; all essences are divine, and there is no absolute existence besides that of God. To most Muslim scholars, the science of tawhid is the systematic theology through which a better knowledge of God may be reached, but to the Ṣūfīs, knowledge of God can be reached only through religious experience and direct vision.