“Watch out!” Jesus told them. “Beware of the yeast of the Pharisees and Sadducees.” Matthew 16:6

The disciples talked this over and said to each other, “He must be saying this because we didn’t bring along any bread.” But Jesus, aware of this, said, “O you of little faith, why are you discussing among yourselves the fact that you have no bread? Then they understood that he was not telling them to guard against the yeast used in bread, but against the teaching of the Pharisees and Sadducees. Matthew 16:12