1 Corinthians 5 (New International Version)

Expel the Immoral Brother!
 1It is actually reported that there is sexual immorality among you, and of a kind that does not occur even among pagans: A man has his father's wife. 2And you are proud! Shouldn't you rather have been filled with grief and have put out of your fellowship the man who did this? 3Even though I am not physically present, I am with you in spirit. And I have already passed judgment on the one who did this, just as if I were present. 4When you are assembled in the name of our Lord Jesus and I am with you in spirit, and the power of our Lord Jesus is present, 5hand this man over to Satan, so that the sinful nature may be destroyed and his spirit saved on the day of the Lord.

 6Your boasting is not good. Don't you know that a little yeast works through the whole batch of dough? 7Get rid of the old yeast that you may be a new batch without yeast—as you really are. For Christ, our Passover lamb, has been sacrificed. 8Therefore let us keep the Festival, not with the old yeast, the yeast of malice and wickedness, but with bread without yeast, the bread of sincerity and truth.

 9I have written you in my letter not to associate with sexually immoral people— 10not at all meaning the people of this world who are immoral, or the greedy and swindlers, or idolaters. In that case you would have to leave this world. 11But now I am writing you that you must not associate with anyone who calls himself a brother but is sexually immoral or greedy, an idolater or a slanderer, a drunkard or a swindler. With such a man do not even eat.

 12What business is it of mine to judge those outside the church? Are you not to judge those inside? 13God will judge those outside. "Expel the wicked man from among you."

From BibleGateway.com: http://www.biblegateway.com/passage/?search=1 Corinthians 5:1-13&version=NIV