'Beware of the Leaven' in the Bible

How is it that you fail to understand that I was not talking to you about bread? But 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 [false] teaching of the Pharisees and Sadducees.

Jesus repeatedly ordered them, saying, “Watch out! Beware of the leaven of the Pharisees and the leaven of Herod.”