MLA
Alexander, Edward Porter, 1835-1910. A printed circular (Columbia, South Carolina), signed by Edwin Porter Alexander requesting official reports, accounts of events, sketches, regimental and other histories, etc. of the First Corps, Army of Northern Virginia to be used in preparation of a history of General James Longstreet's command during the Civil War - September 12, 1866. September 12, 1866. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6042rbp0h5-cor.
APA, 6th edition
Alexander, Edward Porter, 1835-1910. (September 12, 1866)[A printed circular (Columbia, South Carolina), signed by Edwin Porter Alexander requesting official reports, accounts of events, sketches, regimental and other histories, etc. of the First Corps, Army of Northern Virginia to be used in preparation of a history of General James Longstreet's command during the Civil War - September 12, 1866]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6042rbp0h5-cor.
Chicago
Alexander, Edward Porter, 1835-1910, A printed circular (Columbia, South Carolina), signed by Edwin Porter Alexander requesting official reports, accounts of events, sketches, regimental and other histories, etc. of the First Corps, Army of Northern Virginia to be used in preparation of a history of General James Longstreet's command during the Civil War - September 12, 1866, September 12, 1866, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6042rbp0h5-cor.