Romans 3:20
This is because no human being can be considered right with God by [obeying] the requirements of a law. [Note: It is difficult to determine the exact sense in which "law" is used in these verses. It may be law generally, or the law of Moses specifically. See Bruce, pages 52-58]. For the knowledge of what sin is comes from the law of Moses.
Romans 7:9
And I was [once] alive before being aware of the law [i.e., complacent and without a sense of guilt]; but when [awareness of] the commandment [not to sin] came, sin sprang to life,
2 Corinthians 7:9-11
Now I am glad, not because you were made sorry, but because your sorrow led you to repent. For you were made sorry from a godly motive, so were not harmed by us in any way.