„God has conferred upon men liberty of their own will, in order that by purity and sinlessness of life they may become like unto God.“
— Pope Sixtus I
As quoted in On Nature and Grace, Ch. 77, by Augustine of Hippo, as translated by Peter Holmes, Robert Ernest Wallis and Benjamin B Warfield in A Select Library of the Nicene and Post-Nicene Fathers of the Christian Church, Vol. 5 (1887), edited by Philip Schaf, p. 148 The quote above is actually from a Pythagorean philosopher. Pelagius attributed the quote to Pope Sixtus, and Augustine followed his lead until he discovered the error. Augustine himself corrects the source of the quote in the "Retractations" section of his book.