MLA

Wharton, Edith, 1862-1937. Bigelow, William. Box 23, folder 720. 1910, n.d.. https://collections.library.yale.edu/catalog/16780817.

APA, 6th edition

Wharton, Edith, 1862-1937. (["Box 23, folder 720"])(1910, n.d.)[Bigelow, William]. https://collections.library.yale.edu/catalog/16780817.