'Beware of the Leaven' in the Bible

And Jesus said to them, Observe and beware of the leaven of the Pharisees and Sadducees.

Why do you not understand that I spoke to you not of bread, to beware of the leaven of the Pharisees and Sadducees?

Then they understood that he did not tell them to beware of the leaven of bread, but of the teaching of the Pharisees and Sadducees.

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