This paper will focus on the epistemological problem as faced by the founders of Sufism in the 10th and 11th centuries. More than any other Islamic science, Sufism had to prove the legitimacy of its origin, sources, and methods. In particular, Muslim scholars challenged the validity of the Sufi epistemological method of inspiration or self-unveiling (kasf) and concluded that Sufism was not a valid Islamic science. According to the Sufis, after a process of seclusion, a Sufi can remove veils of the carnal (lower) soul (nafs) through the personal process of observation (mushahadah) and can reach the state of mystical annihilation of self (fana). He thus can obtain the inner meanings of the corporeal world and gnostic knowledge directly from God. This enlightenment helps the Sufi not only to receive a deeper knowledge of things such as mystical truth (haqiqa) but also to obtain new knowledge which does not exist explicitly in traditional Islamic sources, the Quran and hadith. Theoreticians of Sufism such as Abu Nasr as-Sarraj (d.988), Abu Talib al-Makkī (d. 996), Abu Bakr al-Kalabadhi (d. 990), al-Qushayrī (d.1072), and al-Hujvīrī (d.1072) emerged between the 10th and 11th centuries and strove to defend the legitimacy of Sufism by identifying out the four aspects of Sufism that were accepted as components of science at that time: subject, method, goal, and terminology. In this paper, I will investigate early Muslim scholars’ critiques of Sufi methodology and the responses of these Sufi scholars. The following research questions lead to a textual conversation between Muslim and Sufi scholars. Why is the Sufi method problematic and invalid in the view of Muslim scholars? How do Sufi scholars claim inspiration as a licit way of obtaining divine knowledge? Where does inspiration rank on the scale of methods for obtaining Islamic knowledge? What is the epistemological significance of Sufi inspiration? By analyzing their answer to these questions, I will highlight the attitudes of Sufi scholars in their efforts to legitimize the Sufi way of knowledge as a licit Islamic method. On the one hand, they were also strict followers of Islamic Law (sharia) who wanted to demonstrate the suitability and reliability of the method. On the other, this was the only way to survive against the critiques of scholars and the threat of political power.