This research explores the impact of general and specific custom (ʿurf ʿāmm and ʿurf khāṣṣ) on jurisprudential branches within Islamic law, emphasizing its theoretical foundations and applied dimensions. The principle “al-ʿādatu muḥakkamah” (custom is authoritative) is widely recognized in both Shāfiʿī and Ḥanafī schools, and serves as a framework for understanding how customs function as a source of rulings. The study first clarifies the definitions of general and specific ʿurf, the groups of people to whom each applies, and the distinctions between them. It further investigates how jurists and uṣūl scholars approached customs when deriving rulings and the extent to which these customs were integrated into legal theory and practice. A critical issue addressed is the misuse of ʿurf, when individuals manipulate it to justify personal desires or prohibit what they dislike. The study raises pressing questions, such as: What are the criteria for distinguishing between general and specific ʿurf? How should jurists act when ʿurf contradicts language or explicit religious texts? What is the ruling regarding newly emerging customs in modern contexts? By employing an inductive-analytical methodology, the research traces the applications of this rule across classical and contemporary scholarship, analyzing scholarly statements and their implications in today’s legal challenges. The study concludes that while ʿurf remains a valid and dynamic source of law, its authority is bound by strict conditions and cannot be applied indiscriminately. Jurists must ensure that customs align with Sharīʿah principles and do not contradict explicit texts, ensuring a balance between flexibility and adherence to divine law.