Matthew 16:5-12 NIV
When they went across the lake, the disciples forgot to take bread. “Be careful,” Jesus said to them. “Be on your guard against the yeast of the Pharisees and Sadducees.”
They discussed this among themselves and said, “It is because we didn’t bring any bread.”
Aware of their discussion, Jesus asked, “You of little faith, why are you talking among yourselves about having no bread? Do you still not understand? Don’t you remember the five loaves for the five thousand, and how many basketfuls you gathered? Or the seven loaves for the four thousand, and how many basketfuls you gathered? How is it you don’t understand that I was not talking to you about bread? But be on your guard against the yeast of the Pharisees and Sadducees.” Then they understood that he was not telling them to guard against the yeast used in bread, but against the teaching of the Pharisees and Sadducees.
NIV: New International Version