MLA

Dei, Johannes de, ca. 1190-1267. Liber poenitentiarius. [between 1300-1400].. https://collections.library.yale.edu/catalog/10621945.

APA, 6th edition

Dei, Johannes de, ca. 1190-1267. ([between 1300-1400].)[Liber poenitentiarius]. https://collections.library.yale.edu/catalog/10621945.