MLA

Steinberg, Saul, 1914-1999. Sterne, Hedda, 1910-2011. Box 46, folder 835-838 | Box 47, folder 839-851 | Box 48, folder 852-855. 1943-circa 1992, undated. https://collections.library.yale.edu/catalog/2005866.

APA, 6th edition

Steinberg, Saul, 1914-1999. (["Box 46, folder 835-838 | Box 47, folder 839-851 | Box 48, folder 852-855"])(1943-circa 1992, undated)[Sterne, Hedda, 1910-2011]. https://collections.library.yale.edu/catalog/2005866.