In De utilitate credendi (“On the profit of believing,” or else “The usefulness of belief” as another translation I have puts it), St Augustine writes on the relationship of faith and reason (Burleigh, 288). In the latter part of §4 we see that he was no proto-Protestant, no matter what some folks might say to the contrary.
I venture to anticipate that, in this hope, wherein I hope that you will hold with us the way of wisdom, He will not fail me, unto Whom I have been consecrated; Whom day and night I endeavor to gaze upon: and since, by reason of my sins, and by reason of past habit, having the eye of the mind wounded by strokes of feeble opinions, I know that I am without strength, I often entreat with tears, and as, after long blindness and darkness the eyes being hardly opened, and as yet, by frequent throbbing and turning away, refusing the light which yet they long after; specially if one endeavor to show to them the very sun; so it has now befallen me, who do not deny that there is a certain unspeakable and singular good of the soul, which the mind sees; and who with tears and groaning confess that I am not yet worthy of it. He will not then fail me, if I feign nothing, if I am led by duty, if I love truth, if I esteem friendship, if I fear much lest you be deceived. [Emphasis added]
St Augustine does not hold to any false notions of salvation by faith alone. He knew as a Christian that he had a duty to obey God, and to strive after holiness, and that if he forsook those duties he could not be saved. He was not a Protestant. He was a Catholic.