This article discusses methods of proving the existence of God in Islamic rational / philosophical theology (Kalam) in the context of attempts to logically justify the Islamic mutakallim theologians of the Koran's position about God as the origin and cause of creation. Along with the argument from the origin of the world (cosmological proof), which was the main form of argument for Islamic theologians, arguments representing variants of teleological proof are considered. In the XI-XII centuries. traditional Kalam methods of substantiation of the existence of God began to be supplemented with evidence drawn from the Arab-Muslim peripatetism (falsafa). Some Muslim mutakallim theologians (al-Juwayni, al-Ghazali) combined Kalam proofs of the existence of God with arguments borrowed from falsaf, such as the argument from the finiteness of the causal series. The influence of Kalam on Islamic traditionalism can be seen in the proof of the existence of God proposed by Ibn Taymiyyah, one of the major Islamic traditionalist theologians. Contrary to the declarative rejection of theological research, Ibn Taymiyyah relied not only on revelatory sources (the Qur'an and the Muslim tradition (Sunnah)), but also resorted to a rational method in justifying the existence of God.