MLA

Edwards, Jonathan, 1703-1758. 1. 1749 Mar 17. Willison, John. Transcript of a letter to JE, in an unidentified hand.. Box 4, folder 149. 1749 March 17. https://collections.library.yale.edu/catalog/33306405.

APA, 6th edition

Edwards, Jonathan, 1703-1758. (["Box 4, folder 149"])(1749 March 17)[1. 1749 Mar 17. Willison, John. Transcript of a letter to JE, in an unidentified hand.]. https://collections.library.yale.edu/catalog/33306405.