MLA
Lee, Robert E. (Robert Edward), 1807-1870. Letter from Confederate General Robert E. Lee (Richmond, Virginia) to Confederate General James Longstreet - August 31, 1863 (typescript). August 31, 1863. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/467jq2bwrc-cor.
APA, 6th edition
Lee, Robert E. (Robert Edward), 1807-1870. (August 31, 1863)[Letter from Confederate General Robert E. Lee (Richmond, Virginia) to Confederate General James Longstreet - August 31, 1863 (typescript)]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/467jq2bwrc-cor.
Chicago
Lee, Robert E. (Robert Edward), 1807-1870, Letter from Confederate General Robert E. Lee (Richmond, Virginia) to Confederate General James Longstreet - August 31, 1863 (typescript), August 31, 1863, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/467jq2bwrc-cor.