MLA

Stein, Gertrude, 1874-1946. Stein, Leo. Box 124, folder 2711-2715. 1895-1920, n.d.. https://collections.library.yale.edu/catalog/17105772.

APA, 6th edition

Stein, Gertrude, 1874-1946. (["Box 124, folder 2711-2715"])(1895-1920, n.d.)[Stein, Leo]. https://collections.library.yale.edu/catalog/17105772.