I don't know the quote, but if it's a statement made by Augustine there's probably a good chance it's from his work De haeresibus.

I don't know the origin of the quote, but I can tell you it's pompous tripe, and here's why:

"Truths" don't belong to churches. Truth was around long before churches and monotheism were yet sparkles in the schizotypal pagan eye, and truth will be around long after religion and superstition of all kinds fall out of human affection. "Truth" actually belongs to those who are willing to open their eyes instead of being arrogantly led around by a nose ring of fear and guilt. Those who would lead others by said nose ring, such as through proclamations that all worthy truth originates solely with god and in the bible, are narrow minded idiots.

If you believe that God created everything, and the words in (whichever) bible are the unquestionable ultimate truths of the universe, then naturally you're going to look at any non-Christian group with any measure of success and accuse them of intellectual theft. It's only natural. "Hey, you heretics stole the idea of not murdering people from Jesus!"

In reality religions have always re-purposed "truth" toward their own ends, especially moral truth. Religion inherently mimics and manipulates the evolving moral truth of its age calls it sacred; all the "truth" contained in Christianity was actually derived by individuals, and added to the changing Christian doctrine over time. But like frogs in slow-boiling pots, many Christians lose themselves in the moment and foolishly reckon that all truth that is presently contained in christian doctrines, interpretations, and Christian minds at large was always there, was put there directly by god, and is the only valid source of knowledge and truth that can possibly exist.

Pompous, narrow minded, idiotic, and arrogant tripe.