MLA
Evans, Clement A. Letter from Clement A. Evans to [Unknown]. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 8, Folder 23. https://digital.library.emory.edu/purl/706g1jwtj2-cor.
APA, 6th edition
Evans, C. A. Letter from Clement A. Evans to [unknown] (Box 8, Folder 23) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/706g1jwtj2-cor.
Chicago
Evans, Clement A. “Letter from Clement A. Evans to [Unknown].” Letters (correspondence). Civil War Collection, n.d. Box 8, Folder 23. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/706g1jwtj2-cor.