MLA

Hughes, Langston, 1902-1967. Abbott, Robert S.. Box 466, folder 11316. n.d.. https://collections.library.yale.edu/catalog/2005553.

APA, 6th edition

Hughes, Langston, 1902-1967. (["Box 466, folder 11316"])(n.d.)[Abbott, Robert S.]. https://collections.library.yale.edu/catalog/2005553.