6 But when that woman was left alone, and all they had gone out, He raised His eyes to the woman. We have heard the voice of justice, let us also hear the voice of clemency. For I suppose that woman was the more terrified when she had heard it said by the Lord, “He that is without sin of you, let him first cast a stone at her.” But they, turning their thought to themselves, and by that very withdrawal having confessed concerning themselves, had left the woman with her great sin to Him who was without sin.
And because she had heard this, “He that is without sin. let him first cast a stone at her,” she expected to be punished by Him in whom sin could not be found. But He, who had driven back her adversaries with the tongue of justice, raising the eyes of clemency towards her, asked her, “Hath no man condemned you?” She answered, “No man, Lord.” And He said, “Neither do I condemn you;” by whom, perhaps, you feared to be condemned, because in me you have not found sin. “Neither will I condemn you.”
What is this, O Lord? Do You therefore favor sins? Not so, evidently. Mark what follows: “Go, henceforth sin no more.” Therefore the Lord did also condemn, but condemned sins, not man. For if He were a patron of sin, He would say, Neither will I condemn you; go, live as you will: be secure in my deliverance; how much soever you will sin, I will deliver you from all punishment even of hell, and from the tormentors of the infernal world. He said not this.
Source: Tractates on the Gospel of John (New Advent)