MLA

Steinberg, Saul, 1914-1999. Steinberg, Moritz. Box 46, folder 823. 1952-1960, undated. https://collections.library.yale.edu/catalog/10055465.

APA, 6th edition

Steinberg, Saul, 1914-1999. (["Box 46, folder 823"])(1952-1960, undated)[Steinberg, Moritz]. https://collections.library.yale.edu/catalog/10055465.