MLA

Steinberg, Saul, 1914-1999. "Steinberg Book - Sept". Box 59, folder 1083. 1950 June 17. https://collections.library.yale.edu/catalog/32366480.

APA, 6th edition

Steinberg, Saul, 1914-1999. (["Box 59, folder 1083"])(1950 June 17)["Steinberg Book - Sept"]. https://collections.library.yale.edu/catalog/32366480.