MLA
Gonne, Maud, 1866-1953. Letter written by Maud Gonne to William Butler Yeats - March 20 [1915]. March 20, 1915. Maud Gonne and W.B. Yeats Papers, circa 1890-1938. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/129p2ngh53-cor.
APA, 6th edition
Gonne, Maud, 1866-1953. (March 20, 1915)[Letter written by Maud Gonne to William Butler Yeats - March 20 [1915]]. Maud Gonne and W.B. Yeats Papers, circa 1890-1938, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/129p2ngh53-cor.
Chicago
Gonne, Maud, 1866-1953, Letter written by Maud Gonne to William Butler Yeats - March 20 [1915], March 20, 1915, Maud Gonne and W.B. Yeats Papers, circa 1890-1938, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/129p2ngh53-cor.