Matthew 16:6, 11-12

Jesus said to them, Be careful and on your guard against the leaven (ferment) of the Pharisees and Sadducees.

How is it that you fail to understand that I was not talking to you about bread? But beware of the leaven (ferment) of the Pharisees and Sadducees. Then they discerned that He did not tell them to beware of the leaven of bread, but of the teaching of the Pharisees and Sadducees.