In the history of Islamic thought, there has been different methods for proving religious beliefs and the way of understanding and interpreting the verses and hadiths related to Islamic m’arif. In understanding religion, sometimes it is emphasized on reason, sometimes on narration and sometimes on both. Ibn Taymiyyah, a theologian and jurist of the seventh century, has an extreme approach in denial of reason and its application in understanding Islamic m’arif. This viewpoint is caused by his principles and presuppositions on the one hand, and on the other hand, it is for avoiding rationalist consequences. Ibn Taymiyyah’s ideas were faced with conflict of the majority of his contemporary scholars; but, some of his apprentices extended his ideas that brought about a very significant role in formation of Salafism, Wahhabism and extremist groups. According to Ibn Taymiyyah, there is no credit for reason neither in the stage of proving religious beliefs nor in understanding and interpreting religious texts. He emphasizes on the means of “nature” in proving the religious beliefs; but, he does not provide a right interpretation of it. Also, he puts emphasis on mystic understanding of the Quran’s appearances, tradition, and beliefs of those called salaf-e saleh, and avoids any type of text interpretation even in opposition with explicit judgment of reason. It seems that, not only his intellectual principles in proving and explaining religious m’arif and his extremist reliance on appearances of divine theology and thoughts of the early Muslims, salaf-e saleh, are void of rational justification, but also they will bring about undesirable results.