MLA

Whitman, Walt, 1819-1892. November Boughs, page proofs. Box 1, folder 6. 1888 Oct 1. https://collections.library.yale.edu/catalog/2053640.

APA, 6th edition

Whitman, Walt, 1819-1892. (["Box 1, folder 6"])(1888 Oct 1)[November Boughs, page proofs]. https://collections.library.yale.edu/catalog/2053640.