MLA
Early, John, 1786-1873. Letter from John Early (Lynchburg, Virginia) to Robert Paine (Aberdeen, Mississippi) - March 23, 1861. March 23, 1861. Robert Paine Papers, 1828-1882. Pitts Theology Library. https://digital.library.emory.edu/purl/706g1jwv1z-cor.
APA, 6th edition
Early, John, 1786-1873. (March 23, 1861)[Letter from John Early (Lynchburg, Virginia) to Robert Paine (Aberdeen, Mississippi) - March 23, 1861]. Robert Paine Papers, 1828-1882, Pitts Theology Library. https://digital.library.emory.edu/purl/706g1jwv1z-cor.
Chicago
Early, John, 1786-1873, Letter from John Early (Lynchburg, Virginia) to Robert Paine (Aberdeen, Mississippi) - March 23, 1861, March 23, 1861, Robert Paine Papers, 1828-1882, Pitts Theology Library. https://digital.library.emory.edu/purl/706g1jwv1z-cor.