MLA

Whitman, Walt, 1819-1892. Manuscript poster. Box 3, folder 147. [ca. 1865]. https://collections.library.yale.edu/catalog/2053779.

APA, 6th edition

Whitman, Walt, 1819-1892. (["Box 3, folder 147"])([ca. 1865])[Manuscript poster]. https://collections.library.yale.edu/catalog/2053779.