One of my friends pointed out to me a quotation attributed to Augustine, but which didn't sound Augustinian. My friend's suspicions were correct. The quotation in question was this: "Doubt is an element of faith."
I found this attributed to Augustine in a number of sources:
"Doubt, as Saint Augustine wrote, is actually an element of faith." Immersion Bible Studies: 1 & 2 Corinthians, James L. Evans (2011), Section 4, "Hope Really Does Float" at 1 Corinthians 15-16.
"St. Augustine: 'Doubt is but another element of faith.'" and "Augustine could say, 'Doubt is but another element of faith.'" Faith and Reason, William Hemsworth (2009).
"Saint Augustine, early in the first millennium, wrote that 'doubt is but another element of faith.'" Baseball as a Road to God: Seeing Beyond the Game (2013), John Sexton et al., Third Inning "Doubt".
"St. Augustine: 'Doubt is but another element of faith.'" Doubting Toward Faith: The Journey to Confident Christianity (2015), Bobby Conway, p. 35.
"As St. Augustine said, 'Doubt is but another element of faith,' so for some deeply religious people, the absence of doubt is not the best measure of religious commitment." Robert D. Putnam and David E. Campbell, American Grace: How Religion Divides and Unites Us, p. 19
"'I've told you what Saint Augustine said about not taking Bible completely literally—and "doubt is but another element of faith."'" Kurt Andersen, "True Believers: a Novel," (2012) p. 59.
The actual source for this quotation, however, is Paul Tillich. Ironically, the Baseball book above actually noticed the same thought in Tillich but apparently didn't realize that Tillich was the original source. Tillich wrote: "But doubt is not the opposite of faith; it is an element of faith." (Systematic Theology, 1975, vol. 2, p. 116) The quotation falsely attributed to Augustine (never with any actual citation to Augustine's works) is actually just a slight rewording of what Tillich wrote.
I'm not sure exactly how the misquotation began. One possibility is someone misreading Kent Smith's "Faith: reflections on experience, theology, and fiction" where the quotation from Tillich comes shortly after a mention of Augustine (p. 2). Even more probably, the phrase got stuck in someone's mind as a pithy quotation. That person then later couldn't remember who actually said it, and assumed that a pithy quotation like that would have come from a smart guy, and consequently named Augustine as the source.
I'm constantly trying to call folks who write to a higher standard of scholarship, particularly when it comes to use of sources. If you quote something from someone, make the effort to track down your source. If you read something in a book that lacks citations, take it with a grain of salt. It may be right, but a lot of books without citations are poorly researched from other secondary sources, also without source citations. I have no reason to suppose that the original source of this misquotation had any malice. Still, this kind of false attribution can lead to problems that go beyond the original mis-attribution.