MLA

Stein, Gertrude, 1874-1946. Boiffard, Jeanne. Box 136, folder 3093. 1946 Aug 9. https://collections.library.yale.edu/catalog/17105788.

APA, 6th edition

Stein, Gertrude, 1874-1946. (["Box 136, folder 3093"])(1946 Aug 9)[Boiffard, Jeanne]. https://collections.library.yale.edu/catalog/17105788.