This letter from Phillis Wheatley to Mary (Clap) Wooster written on 15 July 1778 contains an elegy on the death of Mary's husband, General David Wooster, who died in battle at Ridgefield, Connecticut, 27 April 1777.
This poem is known for its lines concerning slavery in the hero's prayer at the end:
"But how, presumptuous shall we hope to find/ Divine acceptance with th' Almighty mind -- / While yet (O deed ungenerous!) they disgrace/ And hold in bondage Afric's blameless race..."
Gen. Wooster was an acquaintance of Phillis who had previously written to him in 1773 about generating sales of her book, Poems on Various Subjects.
(See the online presentation of the letter Wheatley wrote to Col. Wooster