MLA
Lee, George Washington Custis, 1832-1913. Letter from George Washington Curtis Lee (Lexington, Virginia) to James Longstreet - July 15, 1879 (typescript). July 15, 1879. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/836547d8z4-cor.
APA, 6th edition
Lee, George Washington Custis, 1832-1913. (July 15, 1879)[Letter from George Washington Curtis Lee (Lexington, Virginia) to James Longstreet - July 15, 1879 (typescript)]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/836547d8z4-cor.
Chicago
Lee, George Washington Custis, 1832-1913, Letter from George Washington Curtis Lee (Lexington, Virginia) to James Longstreet - July 15, 1879 (typescript), July 15, 1879, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/836547d8z4-cor.