MLA
Foster, Robert Sanford, 1834-1903. Letter from Robert S. Foster (Camp of the 100th Pennsylvania Volunteer Infantry near Petersburg, Virginia) to his "Dear Sister", Ellen Foster (Homewood, Pennsylvania). Robert S. Foster served in the 100th Pennsylvania Infantry Regiment, Company D - January 26, 1865 (typescript). January 26, 1865. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/945cc2fs45-cor.
APA, 6th edition
Foster, Robert Sanford, 1834-1903. (January 26, 1865)[Letter from Robert S. Foster (Camp of the 100th Pennsylvania Volunteer Infantry near Petersburg, Virginia) to his "Dear Sister", Ellen Foster (Homewood, Pennsylvania). Robert S. Foster served in the 100th Pennsylvania Infantry Regiment, Company D - January 26, 1865 (typescript)]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/945cc2fs45-cor.
Chicago
Foster, Robert Sanford, 1834-1903, Letter from Robert S. Foster (Camp of the 100th Pennsylvania Volunteer Infantry near Petersburg, Virginia) to his "Dear Sister", Ellen Foster (Homewood, Pennsylvania). Robert S. Foster served in the 100th Pennsylvania Infantry Regiment, Company D - January 26, 1865 (typescript), January 26, 1865, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/945cc2fs45-cor.