Pharisees & Sadducees try to test Jesus; Jesus warns his disciples - Read (Matthew 16:1-12, Mark 8:11-21)
The Pharisees and Sadducees came to test Jesus and asked him to show them a sign from heaven. Calling them hypocrites, he told them that they were clever enough to predict the weather looking at the sky, but they could not discern the signs of the times. Calling them a wicked and adulterous generation, he told them that no sign shall be given to them except the sign of the prophet Jonah. (Matthew doesn't detail the sign here, because he did it in Chapter 12:38-40). Jesus then left them and departed.
Later Jesus warned his disciples, "Beware of the leaven of the Pharisees and the Sadducees." They reasoned among themselves, saying, "It is because we have taken no bread." Jesus, being aware of their discussion, said to them, "O you of little faith, why do you reason among yourselves because you have brought no bread? Do you not yet understand, or remember the five loaves of the five thousand and how many baskets you took up? Nor the seven loaves of the four thousand and how many large baskets you took up? How is it you do not understand that I did not speak to you concerning bread, but to beware of the leaven of the Pharisees and Sadducees." Then they understood that he did not tell them to beware of the leaven of bread, but of the doctrine of the Pharisees and Sadducees.