1 Corinthians 5:6-8 New Revised Standard Version (NRSV)
6 Your boasting is not a good thing. Do you not know that a little yeast leavens the whole batch of dough? 7 Clean out the old yeast so that you may be a new batch, as you really are unleavened. For our paschal lamb, Christ, has been sacrificed. 8 Therefore, let us celebrate the festival, not with the old yeast, the yeast of malice and evil, but with the unleavened bread of sincerity and truth.