The Caliphate of Ḥamdallāhi, located in the modern Republic of Mali, was founded by Aḥmad Lobbo in 1818 and left behind a huge corpus of Arabic correspondence and dispatches that is mainly unexplored by historians. This corpus, composed of documents related to the internal administration of the state as well as its relations with other contemporary political entities, is the result of the extensive spread of literacy in Arabic in the territories controlled by the Ḥamdallāhi central authority and its effort to establish itself as a legitimate regional power in West Africa. Among these documents is the Risāla fī ẓuhūr al-khaliīfa al-thānī ʻashar (“Letter on the appearance of the twelfth caliph”) written by Aḥmad Lobbo’s close counselor Nūḥ b. al-Ṭāhir. This document, briefly introduced by Felix Dubois in the late 19th century, has been neglected by scholars, who have discarded it because it includes an obvious forgery. The letter comprises extensive quotes from the Tārīkh al-Fattāsh, allegedly written in the early 16th century by the Timbuktu-based scholar Maḥmūd Kaʻti but actually composed by Nūḥ b. al-Ṭāhir himself. The purpose of the document is to provide political legitimacy to Aḥmad Lobbo through a prophecy that identifies him as the legitimate and supreme Muslim authority for West Africa, by virtue of being the inheritor of the late 15th century–early 16th century Songhay king Askiyà al-ḥājj Muḥammad, the twelfth caliph mentioned by the Prophet Muḥammad in a famous ḥadīth, and mujaddid, or the “renewer” of Islam. With this article, I edit and translate Nūḥ b. al-Ṭāhir’s Risāla and discuss it in the context of the tension between the Caliphate of Ḥamdallāhi and Sokoto. I also discuss the importance of this document in understanding the complex history of the Tārīkh al-Fattāsh.