MLA

Benedict, Saint, and Abbot of Monte Cassino. De Pestilentia. Nicolaus Philippi and Marcus Reinhart, 0AD. https://collections.library.yale.edu/catalog/16986882.

APA, 6th edition

Benedict, S., & of Monte Cassino, A. (0 C.E.). De pestilentia [Early works to 1800, Incunabula in Yale Library]. Nicolaus Philippi and Marcus Reinhart. https://collections.library.yale.edu/catalog/16986882.