The majority of Muslim's philosophers as Ibn Sina and Al-Fârâbî supported the Aristotelian conception of time, they also used it as an argument in their demonstration of the world's eternity. On the contrary, Muslim theologians (mutakallimūn) denied completely the existence of time, and affirmed the thesis of the world's beginning. Fakhr al-Din al-Râzî as a disciple of Ashʿarite school, and influenced by Avicenna's Philosophy, criticized both, philosophical and theological conception of time. So he refused to deny the existence of time, and the Aristotle theory which defines time as a kind of number, or something dependent on change. In this study we will discuss how and why he falsifies these two conceptions concerning the essence of time.