Nicene and Post-Nicene Fathers, Vol. IV:
Writings in Connection with the Donatist Controversy.: Chapter 9

Chapter 9.—10.  Therefore, as I have often said before, and am desirous to bring home to you, whatsoever we may be, you are safe, who have God for your Father and His Church for your mother.  For although the goats may feed in company with the sheep, yet they shall not stand on the right hand; although the chaff may be bruised together with the wheat, it shall not be gathered into the barn; although the bad fish may swim in company with the good within the Lord’s nets, they shall not be gathered into vessels.  Let no man make his boast even in a good man:  let no man shun the good gifts of God even in a bad man.