MLA

Marks, Henry Stacy, 1829-1898. Sambo's testimonial. 1885 November 25. https://collections.library.yale.edu/catalog/2057709.

APA, 6th edition

Marks, Henry Stacy, 1829-1898. (1885 November 25)[Sambo's testimonial]. https://collections.library.yale.edu/catalog/2057709.