MLA
Lee, Robert E. (Robert Edward), 1807-1870. General Order No. 9 - the Confederate surrender of the Army of Northern Virginia to Union General Ulysses S. Grant (photocopy). April 10, 1865. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/10966t1h4m-cor.
APA, 6th edition
Lee, Robert E. (Robert Edward), 1807-1870. (April 10, 1865)[General Order No. 9 - the Confederate surrender of the Army of Northern Virginia to Union General Ulysses S. Grant (photocopy)]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/10966t1h4m-cor.
Chicago
Lee, Robert E. (Robert Edward), 1807-1870, General Order No. 9 - the Confederate surrender of the Army of Northern Virginia to Union General Ulysses S. Grant (photocopy), April 10, 1865, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/10966t1h4m-cor.