MLA
Butler, Benjamin F. (Benjamin Franklin), 1818-1893. Letter from Union general Benjamin Franklin Butler to Dr. George Luckley. Butler was the Union commander of the Department and Army of the Gulf in 1862, and the Army of the James in 1864 - May 28, 1866. May 28, 1866. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/986b2rbq3c-cor.
APA, 6th edition
Butler, Benjamin F. (Benjamin Franklin), 1818-1893. (May 28, 1866)[Letter from Union general Benjamin Franklin Butler to Dr. George Luckley. Butler was the Union commander of the Department and Army of the Gulf in 1862, and the Army of the James in 1864 - May 28, 1866]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/986b2rbq3c-cor.
Chicago
Butler, Benjamin F. (Benjamin Franklin), 1818-1893, Letter from Union general Benjamin Franklin Butler to Dr. George Luckley. Butler was the Union commander of the Department and Army of the Gulf in 1862, and the Army of the James in 1864 - May 28, 1866, May 28, 1866, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/986b2rbq3c-cor.