'Beware of the Leaven' in the Bible

And Jesus said to them, "Watch out for and beware of the leaven of the Pharisees and Sadducees!"

How do you not understand that I did not speak to you about bread? But 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.

And he ordered them, saying, "Watch out! Beware of the leaven of the Pharisees and the leaven of Herod!"