MLA
Wesley, Charles, 1707-1788. Letter from Charles Wesley to "Dear Sister," Ursula Wesley, the foundry on windmill-hill near Moorfields, London - April 16, 1740. April 16, 1740. Wesleyana Collection. Pitts Theology Library. https://digital.library.emory.edu/purl/8708w9gjgk-cor.
APA, 6th edition
Wesley, Charles, 1707-1788. (April 16, 1740)[Letter from Charles Wesley to "Dear Sister," Ursula Wesley, the foundry on windmill-hill near Moorfields, London - April 16, 1740]. Wesleyana Collection, Pitts Theology Library. https://digital.library.emory.edu/purl/8708w9gjgk-cor.
Chicago
Wesley, Charles, 1707-1788, Letter from Charles Wesley to "Dear Sister," Ursula Wesley, the foundry on windmill-hill near Moorfields, London - April 16, 1740, April 16, 1740, Wesleyana Collection, Pitts Theology Library. https://digital.library.emory.edu/purl/8708w9gjgk-cor.