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.
Orison Swett Marden (1896). “Pushing to the Front: Or Success Under Difficulties, a Book of Inspiration and Encouragement to All who are Struggling for Self-elevation Along the Paths of Knowledge and of Duty”