On the apparently severe word that one born of God 'doth not commit sin.' Wesley distinguishes between voluntary sin (which is impossible to one who walks in the Spirit) and involuntary failings (which remain even in mature believers).
Sermon 19 of 44 · 1748 · 1 John 3:9
The Great Privilege of Those that are Born of God
A passage from the sermon
Whosoever is born of God, while he abideth in faith and love, and in the Spirit of prayer and thanksgiving, not only doth not commit sin, but is, in one sense, not capable of doing it. So long as that 'seed which remaineth in him,' that loving, praying, thankful faith, compels him to walk in all simplicity before God, he cannot voluntarily transgress any command of God.
But every one of us is in danger, every moment, of losing this faith — by hearkening to the wrong voice. And whosoever doth so will assuredly fall, sooner or later, into outward sin. Watch and pray, therefore, that ye enter not into temptation.
The full sermon is in the public domain and freely available from CCEL and other archives.