Matthew 16:1, 6, 12

Now the Pharisees and Sadducees came up, and testing Jesus [to get something to use against Him], they asked Him to show them a sign from heaven [which would support His divine authority].

Jesus said to them, “Watch out and be on your guard against 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.