MLA

Hughes, Langston, 1902-1967. Rustin, Bayard. Box 139, folder 2599. 1960 Dec 3. https://collections.library.yale.edu/catalog/17020458.

APA, 6th edition

Hughes, Langston, 1902-1967. (["Box 139, folder 2599"])(1960 Dec 3)[Rustin, Bayard]. https://collections.library.yale.edu/catalog/17020458.