1 Corinthians 5:6 in the World English Bible
Your boasting is not good. Don’t you know that a little yeast leavens the whole lump?
Context
5 To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
6 Your glorying is not good. Know ye not that a little leaven leaveneth the whole lump?
7 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: