According to Muslim mystics, monotheism is compatible with the theory of unity of existence (waḥdat al-wujūd). Some Muslim jurists believe that this amounts to the disbelief in Islam, considering its advocates as disbelievers and impure. In order to elucidate the problem, this paper seeks to elaborate the theory of “personal unity of existence” in Islamic mysticism, as well as the ruling of some jurists to the effect that advocates of such theory are disbelievers and impure. This paper shows that, from the perspective of Islamic mysticism, existence qua existence is necessary by itself. Therefore, existence is in the true sense of the term only applicable to God. This is not to say that mystics deny the existence of creatures; instead, they attribute existence to creatures figuratively and symbolically, rather than literally. We conclude that, first of all, this contradicts the jurists’ conception of unity of existence, and second, given our explanation of unity of existence, it turns out that the theory does not imply the denial of any essential religious doctrine—indeed, mystics do not deny any essential doctrine.