MLA

Whitman, Walt, 1819-1892. O'Connor, William Douglas to Abby H. Price. Box 2, folder 102. 1866 Jan 11. https://collections.library.yale.edu/catalog/2053736.

APA, 6th edition

Whitman, Walt, 1819-1892. (["Box 2, folder 102"])(1866 Jan 11)[O'Connor, William Douglas to Abby H. Price]. https://collections.library.yale.edu/catalog/2053736.