Matthew 16:6 (KJV)

The Pharisees also with the Sadducees came, and tempting desired him that he would shew them a sign from heaven.

He answered and said unto them, When it is evening, ye say, It will be fair weather: for the sky is red.

And in the morning, It will be foul weather to day: for the sky is red and lowering. O ye hypocrites, ye can discern the face of the sky; but can ye not discern the signs of the times?

A wicked and adulterous generation seeketh after a sign; and there shall no sign be given unto it, but the sign of the prophet Jonas. And he left them, and departed.

And when his disciples were come to the other side, they had forgotten to take bread.

And they reasoned among themselves, saying, It is because we have taken no bread.

Which when Jesus perceived, he said unto them, O ye of little faith, why reason ye among yourselves, because ye have brought no bread?

Do ye not yet understand, neither remember the five loaves of the five thousand, and how many baskets ye took up?

Neither the seven loaves of the four thousand, and how many baskets ye took up?

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