'Beware of the Leaven' in the Bible

Then Jesus said to them, Take heed and beware of the leaven of the Pharisees and of the Sadducees.

How is it that ye do not understand that I spoke not to you concerning bread, that ye should beware of the leaven of the Pharisees and of the Sadducees?

And he charged them saying, Take heed, beware of the leaven of the Pharisees, and of the leaven of Herod.