MLA

Whitman, Walt, 1819-1892. Whitman signature. Box 11, folder 243. n.d.. https://collections.library.yale.edu/catalog/2053866.

APA, 6th edition

Whitman, Walt, 1819-1892. (["Box 11, folder 243"])(n.d.)[Whitman signature]. https://collections.library.yale.edu/catalog/2053866.