Matthew 16:6, 11-12

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

How is it you do not understand that I did not speak to you concerning bread?—but 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 doctrine of the Pharisees and Sadducees.