This paper uses open-source periodicals in Arabic, English, French, and Urdu to examine how authors from the Islamic State of Iraq and Syria (ISIS) and the Taliban construct rival claims of leadership and discredit each other in official periodicals. ISIS authors stress their movement’s legitimacy through religious texts that call for the unity of the Muslim community behind a single leader and jurisprudential texts on the conditions for establishing a caliphate. In contrast, Taliban authors emphasise that all mujahideen groups must stand behind the Taliban in a single united front that has been committed to jihad for decades before ISIS’s emergence and that ISIS fosters disunity through rivalry. Despite belonging to a common Sunni Islamic tradition, both groups apply classical, canonical texts differently to contemporary issues. Their unique interpretations of religious texts to justify claims of leadership can be analysed in order to construct counter-messaging strategies that are compatible with Sunni Islam. This compatibility may dissuade potential recruits who are motivated to act based on religious reasons.