MLA

Whitman, Walt, 1819-1892. Papers relating to George Whitman. Box 1, folder 56. 1864-65. https://collections.library.yale.edu/catalog/2053690.

APA, 6th edition

Whitman, Walt, 1819-1892. (["Box 1, folder 56"])(1864-65)[Papers relating to George Whitman]. https://collections.library.yale.edu/catalog/2053690.