Cross reference
Exodus 13:7
7 unleavened things are eaten the seven days, and any thing fermented is not seen with thee; yea, leaven is not seen with thee in all thy border.
Exodus 12:19
19 seven days leaven is not found in your houses, for any `one' eating anything fermented -- that person hath been cut off from the company of Israel, among the sojourners or among the natives of the land;
Matthew 16:6
6 and Jesus said to them, `Beware, and take heed of the leaven of the Pharisees and Sadducees;'