Luke 17:3 – 5
New International Version (NIV1984)
3 So watch yourselves. “If your brother sins, rebuke him, and if he repents, forgive him. 4 If he sins against you seven times in a day, and seven times comes back to you and says, ‘I repent,’ forgive him.”
5 The apostles said to the Lord, “Increase our faith!”.
From BibleGateway.com: http://www.biblegateway.com/passage/?search=Luke 17:3 – 5&version=NIV