MLA

Hughes, Langston, 1902-1967. Ssou, Philemon. Box 21, folder 305. 1965 November. https://collections.library.yale.edu/catalog/16207082.

APA, 6th edition

Hughes, Langston, 1902-1967. (["Box 21, folder 305"])(1965 November)[Ssou, Philemon]. https://collections.library.yale.edu/catalog/16207082.