Matthew 16:1, 6, 12

One day the Pharisees and Sadducees came to test Jesus, demanding that he show them a miraculous sign from heaven to prove his authority.

“Watch out!” Jesus warned them. “Beware of the yeast of the Pharisees and Sadducees.”

Then at last they understood that he wasn’t speaking about the yeast in bread, but about the deceptive teaching of the Pharisees and Sadducees.