MLA

Hahn, Reynaldo, 1875-1947. Letters to René Peter. Box 1 | 1-15. 1899-1947, undated. https://collections.library.yale.edu/catalog/17316456.

APA, 6th edition

Hahn, Reynaldo, 1875-1947. (["Box 1 | 1-15"])(1899-1947, undated)[Letters to René Peter]. https://collections.library.yale.edu/catalog/17316456.