In 1914 Celal Nuri “?leri” (1881–1938) published his magnum opus, Hatem ül-Enbiya (or The Seal of the Prophets). A critical work of Muslim scholarship, Hatem ül-Enbiya challenged traditional approaches to the prophetic biography genre (siyer/s?ra) in its systematic application of scientific, rational, and “mathematical” methodologies to historical and theological questions. Nuri’s early career coincided with the Second Constitutional Era (1909–1920)—a period when nationalism, modernism, and pan-Islamism competed for public approval and ideological dominance. He believed in the value and place of religion in modern life, and even espoused belief in Islam’s potential as a trans-national unifying force. Nuri was a rare blend of modernist-Islamist, whose beliefs died out by 1922, along with the dissolution of the Ottoman Empire. Under the Turkish Republic, Nuri rebranded himself a secularist and is considered among the young Republic’s ideological founding figures. Hatem ül-Enbiya was Celal Nuri’s attempt at holding Islam’s greatest champion, the Prophet Muhammad, to the scientific and public scrutiny that comprised the highest standard of modern, rational inquiry. Nuri’s work was as much a statement on the validity of modern methods as it was a proclamation of the soundness of Islamic principles. The book drew the criticism of local and regional ulama prior to its publication, which is why its final chapter consists of a preemptive rebuttal entitled “My Response to Detractors,” written and submitted to the press by Nuri in haste. Hatem ül-Enbiya is a significant but forgotten contribution to early twentieth-century Muslim modernist scholarship. This paper examines Hatem ül-Enbiya’s formulation of the Prophet Muhammad and Islam’s rational foundations. Nuri highlights inherently rational framings of Islam to translate the religion’s intrinsic modernity into current sensibilities. Moreover, by grounding Islam’s founder in rationalism and reason, Nuri injects logical mechanisms that would enable the reformation of the religion from the inside out, through a reinvigorated understanding of the Prophet Muhammad as timeless, exemplary human being.