MLA

Ferdinandez, Petrus. Antiphonary for the Cistercian Rite. 1571. https://collections.library.yale.edu/catalog/9998912.

APA, 6th edition

Ferdinandez, P. (1571). Antiphonary for the Cistercian rite [Manuscripts, Renaissance Spain 16th century, Medieval and Renaissance Manuscript Fragments in Beinecke Library, Medieval and Renaissance Manuscripts in Beinecke Library]. https://collections.library.yale.edu/catalog/9998912.