MLA
Gonne, Maud, 1866-1953. Unpublished letter written by Maud Gonne to William Butler Yeats - unknown date. unknown. 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/856n02v996-cor.
APA, 6th edition
Gonne, Maud, 1866-1953. (unknown)[Unpublished letter written by Maud Gonne to William Butler Yeats - unknown date]. 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/856n02v996-cor.
Chicago
Gonne, Maud, 1866-1953, Unpublished letter written by Maud Gonne to William Butler Yeats - unknown date, unknown, Maud Gonne and W.B. Yeats Papers, circa 1890-1938, Stuart A. Rose Manuscript,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/856n02v996-cor.