MLA
Letter from [Unknown] to Confederate General James Longstreet - - June 23, 1863 (Typescript). 1863. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 4, Folder 50. https://digital.library.emory.edu/purl/5053ffbh8g-cor.
APA, 6th edition
Letter from [unknown] to Confederate General James Longstreet - - June 23, 1863 (typescript) (Box 4, Folder 50). (1863). [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/5053ffbh8g-cor.
Chicago
“Letter from [Unknown] to Confederate General James Longstreet - - June 23, 1863 (Typescript).” Letters (correspondence). Civil War Collection, 1863. Box 4, Folder 50. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/5053ffbh8g-cor.