MLA

Haas, Robert Bartlett (1916-2010). Letter from Donald Gallup. Box 5. 1936-1985, undated. https://collections.library.yale.edu/catalog/17173427.

APA, 6th edition

Haas, Robert Bartlett (1916-2010). (["Box 5"])(1936-1985, undated)[Letter from Donald Gallup]. https://collections.library.yale.edu/catalog/17173427.