Quoted in Christian Monitor, and Religious Intelligencer, 4 July 1812. An almost identical quotation by Newton, said to have been uttered "a little before he died," appears in Joseph Spence, Anecdotes, Observations, and Characters of Books and Men, published in 1820 but extant in manuscript form from around 1730. A paraphrase of Newton's words was printed in a note in a 1797 edition of TheWorks of Alexander Pope.
Isaac Newton (1966). “Sir Isaac Newton's Mathematical Principles of Natural Philosophy and His System of the World: The motion of bodies”, p.17, Univ of California Press
Sir Isaac Newton, Florian Cajori (1946). “Sir Isaac Newton's Mathematical Principles of Natural Philosophy and His System of the World”, p.6, Univ of California Press