1 Corinthians 5:5-6

you are to hand over this man to Satan for the destruction of his body, so that his spirit may be saved in the day of the Lord Jesus. Your boasting [over the supposed spirituality of your church] is not good [indeed, it is vulgar and inappropriate]. Do you not know that [just] a little leaven ferments the whole batch [of dough, just as a little sin corrupts a person or an entire church]?