"Let Pelagius confess that it is possible for man to be without sin than in no other way than by the grace of Christ, and we will be at peace with him."
Wow! How come we never hear that quote from Augustine? You always hear about how Augustine believes in original sin, which is true. But, you never hear that he believed in the possibility of such a level of regeneration. So, one could argue that Wesley is more Augustinian than most reformed theologians when it comes to sin in believers! Talk about turning the tables :)
Here is what the Presbyterian Larger Catechism says:
No man is able, either by himself or by any grace received in this life, perfectly to keep the commandments of God, but doth daily break them in thought, word, and deed.
Here is what I John says:
You know that he appeared to take away sins, and in him there is no sin. No one who abides in him sins; no one who sins has either seen him or known him. Little children, let no one deceive you. He who does right is righteous, as he is righteous. He who commits sin is of the devil; for the devil has sinned from the beginning. The reason the Son of God appeared was to destroy the works of the devil. No one born of God commits sin; for God's nature abides in him, and he cannot sin because he is born of God.—I John 3:5-9 RSV
I prefer Augustine here; at least he is scriptural.