'Beware of the Leaven' in the Bible

and therefore when Jesus said to them, Take heed and beware of the leaven of the pharisees and of the sadducees,

How is it then that ye do not understand that I did not speak to you concerning bread, when I bid you to beware of the leaven of the pharisees and of the sadducees?

Then they understood, that He did not bid them beware of the leaven of bread, but of the doctrine of the pharisees and of the sadducees.