MLA

Lindbergh, Charles A. (Charles Augustus), 1902-1974. At Regina Laudis In Bethlehem, Connecticut. 20, folder 8. 1971 August 6. https://collections.library.yale.edu/catalog/10013340.

APA, 6th edition

Lindbergh, Charles A. (Charles Augustus), 1902-1974. (["20, folder 8"])(1971 August 6)[At Regina Laudis In Bethlehem, Connecticut]. https://collections.library.yale.edu/catalog/10013340.