MLA
Preston, Thomas S. Letter from Thomas S. Preston (University of Virginia) to J. W. Weidemayer, Regarding Photograph of William C. Preston. Thomas S. Preston Was Aide to General Stonewall Jackson - April 28, 1888. 1888. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 9, Folder 25. https://digital.library.emory.edu/purl/12683bk4kq-cor.
APA, 6th edition
Preston, T. S. (1888). Letter from Thomas S. Preston (University of Virginia) to J. W. Weidemayer, regarding photograph of William C. Preston. Thomas S. Preston was aide to General Stonewall Jackson - April 28, 1888 (Box 9, Folder 25) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/12683bk4kq-cor.
Chicago
Preston, Thomas S. “Letter from Thomas S. Preston (University of Virginia) to J. W. Weidemayer, Regarding Photograph of William C. Preston. Thomas S. Preston Was Aide to General Stonewall Jackson - April 28, 1888.” Letters (correspondence). Civil War Collection, 1888. Box 9, Folder 25. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/12683bk4kq-cor.