MLA
Lee, Robert E. (Robert Edward), 1807-1870. Letter from Confederate general Robert E. Lee to Jefferson Davis, president of the Confederate States - July 8, 1863 (photocopy). July 8, 1863. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/689d51c6fc-cor.
APA, 6th edition
Lee, Robert E. (Robert Edward), 1807-1870. (July 8, 1863)[Letter from Confederate general Robert E. Lee to Jefferson Davis, president of the Confederate States - July 8, 1863 (photocopy)]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/689d51c6fc-cor.
Chicago
Lee, Robert E. (Robert Edward), 1807-1870, Letter from Confederate general Robert E. Lee to Jefferson Davis, president of the Confederate States - July 8, 1863 (photocopy), July 8, 1863, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/689d51c6fc-cor.