The author of the Arabic theological work Al-Tamhīd fī bayān al-tauḥīd (“Introduction to the explanation of monotheism”), Abū Shakūr al-Sālimī (5th/11th Century), belongs to the theological school in the succession of Abū Manṣūr al-Māturīdī (died 333/944), which forms the second pillar of Sunni confession alongside the doctrines of Abū l-Ḥasan al-Ash'arī (died 324/935) and his followers. In Transoxanian regions, in Turkey, and in the Balkan States, the Māturīdī School still has scores of followers, and the Tamhīd served as an important marker of Sunnī theology into the nineteenth century. However, details of Māturīdite kalām remain insufficiently studied. This deficiency applies to the utilization of texts, partially not yet available in editions, as is the case concerning the Tamhīd. On the other hand, a huge need for research remains, particularly with regard to the relationship between Māturidism and Ash'arism. A particularity with regard to the contents of the Tamhīd is the fact that in this work al-Ash'arī and the al-Ash'arites are for the first time named in Māturīdī writings as Sunnī rivals. Regarding al-Māturīdī, he mainly argued with the exaggerated rationalism of the Mu'tazila. This early Islamic current concentrated on human reason, thus disregarding the Divine omnipotence despite its fundamental importance in Islamic theology. In contrast, al-Ash'ari stresses the role of revelation, so that human reason ultimately becomes irrelevant. Following the argumentation of the Māturidite theologians, this concept is not appropriate to refute the doctrines of the Mu'tazila. They demonstrate that it is rather necessary to account for both human reason and revelation, in order to develop a theological concept that copes with the almighty God and humankind with their rational cognitive faculty.