What is the source of this quote from Augustine about thanking heretics? I am trying to find the source or reference for the following quote by St. Augustine of Hippo (P. S.: I translated this from Arabic, so the verbatim of the English version must be different):

We thank the heretics and &quot;innovators&quot; for what they brought of heresies and doubts against the scripture (bible), that made us understand deeply the scripture, and gain strength in knowledge, and discover treasures that we would not have discovered.
I found out that it is not an exact quote, but like a summary of an article published in:
&quot;St. Augustine: Sermons for Christmas and Epiphany&quot;
Publisher: Longmans, Green And Co., 1952, P. 35
Article: The good that comes of heretics. The good that came through the traitor Judas.