MLA

Wolff, Helen, 1906-1994. Schabert, Kyrill. Box 39, folder 1186-1188. 1958-60, n.d.. https://collections.library.yale.edu/catalog/2021297.

APA, 6th edition

Wolff, Helen, 1906-1994. (["Box 39, folder 1186-1188"])(1958-60, n.d.)[Schabert, Kyrill]. https://collections.library.yale.edu/catalog/2021297.