MLA
General Order No. 9 by Confederate General Robert E. Lee, Headquarters Army of Northern Virginia, Holograph Copy of General Lee's Farewell Message to His Troops, Reported to Be Copied by a Courier of General Lee - April 10, 1865. 1865. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 4, Folder 41. https://digital.library.emory.edu/purl/433dz08mrb-cor.
APA, 6th edition
General Order No. 9 by Confederate General Robert E. Lee, Headquarters Army of Northern Virginia, holograph copy of General Lee's farewell message to his troops, reported to be copied by a courier of General Lee - April 10, 1865 (Box 4, Folder 41). (1865). [Orders (military records)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/433dz08mrb-cor.
Chicago
“General Order No. 9 by Confederate General Robert E. Lee, Headquarters Army of Northern Virginia, Holograph Copy of General Lee's Farewell Message to His Troops, Reported to Be Copied by a Courier of General Lee - April 10, 1865.” Orders (military records). Civil War Collection, 1865. Box 4, Folder 41. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/433dz08mrb-cor.