MLA

McCormick, Purnice, and David H. McGuire. [Autograph Letter Signed Regarding the Purchase of a Slave, 1863 June 4]. 1859. https://collections.library.yale.edu/catalog/11693648.

APA, 6th edition

McCormick, P., & McGuire, D. H. (1859). [Autograph letter signed regarding the purchase of a slave, 1863 June 4] [Autographs, Business records, Correspondence, Notes]. https://collections.library.yale.edu/catalog/11693648.