The issue of divine decree is a significant and complex topic in Islamic philosophy and theology. It has been examined from various philosophical, theological, and ethical perspectives and is frequently accompanied by questions, particularly regarding the role of prayer. The central question this article addresses is: If God has decreed all matters, what is the role of supplication in this framework? If everything is predestined according to divine decree, does supplication hold any benefit for a person, or does it lose its impact because everything is predetermined? Imam Khomeini and Fakhr al-Din al-Razi
are prominent scholars in this field, and this research uses a descriptive and rational analytical method to examine and compare their views. The conclusion is that both Imam Khomeini and Fakhr al-Din al-Razi acknowledge the efficacy of supplication within the system of existence and demonstrate that prayer is not in conflict with divine decree. While both scholars believe in the significance of supplication and its connection to divine decree, they differ in certain aspects. For example, Imam Khomeini links the acceptance of supplication to the fulfilment of certain conditions such as reflection on Qur'anic verses and traditions, while Fakhr al-Din al-Razi, being an Ash'ari theologian, is more inclined towards philosophical determinism, seeing supplication's acceptance as inevitable without such preconditions. Furthermore, Imam Khomeini views supplication as having different degrees, while Fakhr al-Din al-Razi does not hold this belief. This study highlights these differences.