The Kuzari, full title Book of Refutation and Proof on Behalf of the Despised Religion (Arabic: كتاب الحجة والدليل في نصرة الدين الذليل: Kitâb al-ḥujja wa'l-dalîl fi naṣr al-dîn al-dhalîl), also known as the Book of the Khazar (Hebrew: ספר הכוזרי: Sefer ha-Kuzari), is one of the most famous works of the medieval Spanish Jewish philosopher and poet Judah Halevi, completed in the Hebrew year 4900 (1139-40CE).