1 Corinthians 5:6–8

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 sacrificedb for us: 8 Therefore let us keep the feastc, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.