MLA

Whitman, Walt, 1819-1892. Page, Curtis Hidden. Box 1, folder 13. 1908 Sep 15. https://collections.library.yale.edu/catalog/2053647.

APA, 6th edition

Whitman, Walt, 1819-1892. (["Box 1, folder 13"])(1908 Sep 15)[Page, Curtis Hidden]. https://collections.library.yale.edu/catalog/2053647.