MLA
Foster, Robert Sanford, 1834-1903. Letter from Robert S. Foster ("At the Hospitable [sic]") to his "Dear Sister", Ellen Foster (Homewood, Pennsylvania). Robert S. Foster served in the 100th Pennsylvania Infantry Regiment, Company D - October 6, 1864 (typescript). October 6, 1864. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/948sbcc3mf-cor.
APA, 6th edition
Foster, Robert Sanford, 1834-1903. (October 6, 1864)[Letter from Robert S. Foster ("At the Hospitable [sic]") to his "Dear Sister", Ellen Foster (Homewood, Pennsylvania). Robert S. Foster served in the 100th Pennsylvania Infantry Regiment, Company D - October 6, 1864 (typescript)]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/948sbcc3mf-cor.
Chicago
Foster, Robert Sanford, 1834-1903, Letter from Robert S. Foster ("At the Hospitable [sic]") to his "Dear Sister", Ellen Foster (Homewood, Pennsylvania). Robert S. Foster served in the 100th Pennsylvania Infantry Regiment, Company D - October 6, 1864 (typescript), October 6, 1864, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/948sbcc3mf-cor.