MLA

Van Vechten, Carl, 1880-1964. Warfield, William. Box 107, folder 1950. 1951 February 7. https://collections.library.yale.edu/catalog/2028281.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 107, folder 1950"])(1951 February 7)[Warfield, William]. https://collections.library.yale.edu/catalog/2028281.