“Your glorying is not good. Know ye not that a little leaven leaveneth the whole lump? Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us: therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened of sincerity and truth. I wrote unto you in an epistle not to company with fornicators: yet not altogether with the fornicators of this world, or with the covetous, or extortioners, or with idolaters; for then must ye needs go out of the world.
But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolater, or a railer, or a drunkard, or an extortioner; with such an one no not to eat. For what have I to do to judge them also that are without? Do not ye judge them that are within? But them that are without God judgeth. Therefore put away from among yourselves that wicked person.” 1 Corinthians 5:6-13 (KJB)
References: 1 Corinthians 3:21; 2 Timothy 2:17; Exodus 12:15; John 17:15; 1 John 5:19; Deuteronomy 13:5