MLA

Whitman, Walt, 1819-1892. O'Connor, William Douglas. Box 2, folder 84. 1882. https://collections.library.yale.edu/catalog/2053718.

APA, 6th edition

Whitman, Walt, 1819-1892. (["Box 2, folder 84"])(1882)[O'Connor, William Douglas]. https://collections.library.yale.edu/catalog/2053718.