'Beware of the Leaven' in the Bible

And Jesus said to them, Take heed and beware of the leaven of the Pharisees and Saducees.

How do ye not understand, that I spake not to you concerning bread, to beware of the leaven of the Pharisees and Saducees?

Then they understood, that he did not bid them beware of the leaven of bread, but of the doctrine of the Pharisees and Saducees.