This paper discusses the broader historiographical significance of recently published Ibadi texts dated to the 8th century CE. The valuable nature of these works can be demonstrated in their documentation of paradigmatic precepts and conceptual models of philosophical theology or kalam which subsequently went on to have broader influence in Islamic doctrine, exegesis, and law as a whole. Such examples indicate the methodological incumbency of incorporating Ibadi thought for the sake of properly historicizing “reason and revelation” as a category of analysis for Islamic thought. The very bifurcation of reason and revelation as distinct epistemic resources for Islamic theology finds its earliest documentation in the particular text which receives the most attention in this paper: the Radd ‘ala Ibn ‘Umayr by Abd Allah b. Yazid al-Fazari. The juxtaposition of these two resources, their role in the proof of the existence of God and prophethood, and the epistemic role and limits of human thought in determining moral value or religious injunction (which defined more commonly known debates between Mu’tazilites, Ash’aris, and other schools of thought), can all be discerned here in embryo, and likewise accompanied by surprisingly developed argumentation pointing to even earlier developmental stages. This paper offers an exposition of the abovementioned material in conversation with recent discussions by Wilferd Madelung along with a genealogy of its subsequent reception history in later traditions. This will be accompanied by historiographical reflections on the necessity of acknowledgement of these sources beyond specialists in Ibadism to include specialists in Islamic Thought as a whole.