MLA

Petrus, Cantor, approximately 1130-1197. Summa Abel. [between 1200 and 1250].. https://collections.library.yale.edu/catalog/10079796.

APA, 6th edition

Petrus, Cantor, approximately 1130-1197. ([between 1200 and 1250].)[Summa Abel]. https://collections.library.yale.edu/catalog/10079796.