MLA

Ward, Frederick Townsend, 1831-1862. Formal notes exchanged between the parents of bride and groom when a marriage is agreed upon [from Fan Sheng-fu to Ward]. Box 1, folder 19. undated. https://collections.library.yale.edu/catalog/10020622.

APA, 6th edition

Ward, Frederick Townsend, 1831-1862. (["Box 1, folder 19"])(undated)[Formal notes exchanged between the parents of bride and groom when a marriage is agreed upon [from Fan Sheng-fu to Ward]]. https://collections.library.yale.edu/catalog/10020622.