MLA

Stein, Gertrude, 1874-1946. Picasso, Pablo. Box 119, folder 2552-2559. 1906-30, n.d.. https://collections.library.yale.edu/catalog/32473625.

APA, 6th edition

Stein, Gertrude, 1874-1946. (["Box 119, folder 2552-2559"])(1906-30, n.d.)[Picasso, Pablo]. https://collections.library.yale.edu/catalog/32473625.