"Then came Peter to him, and said, Lord, how oft shall my brother sin against me, and I forgive him? till seven times? Jesus saith unto him, I say not unto thee, Until seven times: but, Until seventy times seven." Matthew 18:21-22
Great Sermon! What is interesting is that Peter asked the question about forgiving his brother. I guess he didn't mention his enemy or man-on-street, because he thought he would not have to forgive them at all.
This is one of Jesus' Hard Sayings, especially in today's world where everyone is so quick to stand up for their rights, and sue anyone for nearly anything.