MLA

Augustus Frederick, Prince, Duke of Sussex, 1773-1843. Collyer, William Bengo, 1782-1854. ALS to the Duke of Sussex, Peckham. Box 1, folder 31. 1829 Sep 7. https://collections.library.yale.edu/catalog/16684003.

APA, 6th edition

Augustus Frederick, Prince, Duke of Sussex, 1773-1843. (["Box 1, folder 31"])(1829 Sep 7)[Collyer, William Bengo, 1782-1854. ALS to the Duke of Sussex, Peckham]. https://collections.library.yale.edu/catalog/16684003.