Throughout the history of Islam, various scholars have advanced claims asserting that Islamic teachings were borrowed from other traditions, particularly Judaism, citing similarities between the two faiths as evidence for this premise. One such parallelism that might appear to reinforce the claim of Islamic borrowing from Judaism is the relationship between the institution of priesthood (Kehanat) in Judaism and Sayyidhood (Siyadat) in Islam—both of which rely on a lineage-based association connecting priests and Sayyids to prophets within their respective traditions. Employing a comparative analysis approach based on library research, this study examines and contrasts the origin philosophy, functions, as well as the socio-economic dimensions of Jewish priesthood and Islamic Sayyidhood, drawing upon credible primary sources from both religious traditions. The findings of this comparative research demonstrate that despite sharing similarities regarding their "basis of attribution" (lineage by blood), fundamental essential, structural, and foundational distinctions exist between the two institutions. Priesthood in Judaism was an inherited, exclusive office characterized by specific socio-economic functions. Conversely, Sayyidhood in Islam is rooted in devotion to the Prophet Muhammad (PBUH) and the recompense of his prophethood (Ajr al-Risalah), rather than serving as an institution with an exclusive structural hierarchy; accordingly, Sayyids have historically maintained full autonomy in socio-economic affairs. These foundational disparities not only pose a severe challenge to the hypothesis of Islam borrowing teachings from Judaism but effectively disprove it. Overall, this study reveals that despite superficial similarities in lineage attribution, profound essential and functional differences exist between Jewish priesthood and Islamic Sayyidhood, thereby refuting claims of borrowing and affirming the authenticity of Sayyidhood within Islam.