MLA

Whitman, Walt, 1819-1892. Wentworth, Horace. Box 2, folder 88. 1866. https://collections.library.yale.edu/catalog/2053722.

APA, 6th edition

Whitman, Walt, 1819-1892. (["Box 2, folder 88"])(1866)[Wentworth, Horace]. https://collections.library.yale.edu/catalog/2053722.