Shaykh al-Saduq (d. 381 AH), one of the prominent hadith scholars and theologians of the Imamiyya, played an important role in explaining and defending the doctrine of disavowal (tabarri from the opponents of Ahl al-Bayt) . This study aims to revisit the foundations and structure of the doctrine of disavowal within his intellectual framework, with a focus on his theological works, particularly al-I'tiqadat and al-Amali. The research method is textual content analysis based on the verses of the Holy Qur'an, the traditions of the Infallibles, and rational arguments. The findings indicate that Shaykh al-Saduq regarded disavowal not only as a religious obligation but also as a necessary condition for the realization of wilayah and complete faith; to the extent that doubt regarding the Imamate or testimony of the Imams leads to departure from religion and necessitates disavowal of such individuals. Through an integrated approach combining transmitted evidence and reason, he established disavowal as a complement to wilayah and as a doctrinal boundary between Shi'a and their opponents, considering it rationally necessary as well.