Matthew 16:1, 6, 12

The Pharisees and Sadducees came up, and testing Jesus, they asked Him to show them a sign from heaven.

And Jesus said to them, “Watch out and beware of the leaven of the Pharisees and Sadducees.”

Then they understood that He did not say to beware of the leaven of bread, but of the teaching of the Pharisees and Sadducees.