Matthew 16:12

But when he saw many of the Pharisees and Sadducees coming for his baptism, he said to them, “You brood of vipers, who warned you to flee from the wrath to come?

And the Pharisees and Sadducees came, and testing Him, they asked Him to show them a sign from heaven.

“How is it that you do not understand that I did not speak to you concerning bread? But beware of the leaven of the Pharisees and Sadducees.”

At this time, after so many thousands of the crowd had gathered together that they were trampling on one another, He began saying to His disciples first, “Be on your guard for the leaven of the Pharisees, which is hypocrisy.

Your boasting is not good. Do you not know that a little leaven leavens the whole lump?