This paper examines central problems regarding Avicenna’s (d.1037) famous proof for the existence of God and explores how it became a central topic on the agenda of the early modern reformists, including Jamāl al-Dīn al-Afghānī (d.1897) and Muḥammad ‘Abduh (d.1905). The nature of Avicenna’s proof of God has been widely contested in both Islamic intellectual history and contemporary scholarship. H. Davidson (1987) and M. Marmura (1980) argue that the proof is cosmological in nature, while others such as P. Morewedge (1979) and F. Rahman (1963) argue that it is ontological— that is, a proof that proceeds simply from an analysis of the concept of necessary existence without reference to any physical facts about the external world (in contrast to cosmological proofs). However, these works have not considered a version of the proof that appears in Avicenna’s compendium, the Salvation, which goes unmentioned in the literature. My paper examines this version with special attention to what it reveals with respect to the nature of Avicenna’s proof of God. Specifically, I look at his argument that objects in the world require not just a cause to bring them into existence, but a cause to maintain them in existence as well, in order to draw out the a priori or a posteriori nature of the premises he relies on. I argue that his proof is cosmological in nature, depending upon a very particular — and highly contested — cosmology and physics. Avicenna’s proof was important to the modern reformists like ‘Abduh and al-Afghānī who were exploring the classical Islamic intellectual tradition as a response to European philosophical discussions about God and his existence. By closely examining a cryptic but revealing chapter in the Salvation, this paper not only complicates what has become the standard reading of Avicenna’s proof, but sheds light on a largely unexplored gloss by ‘Abduh on an important work on theology. The analysis investigates how ‘Abduh’s positions in the gloss were greatly informed by the philosophical teachings of his guide al-Afghānī.