Mark 8:15

12 And he was very sad in spirit, and said, Why is this generation looking for a sign? truly, I say to you, No sign will be given to this generation.

13 And he went away from them, and again got into the boat and went across to the other side.

14 And they had taken no thought to get bread; and they had only one cake of bread with them in the boat.

15 And he said to them, Take care to be on the watch against the leaven of the Pharisees and the leaven of Herod.

16 And they said to one another, We have no bread.

17 And Jesus, hearing it, said to them, Why are you reasoning among yourselves because you have no bread? do you still not see, and is it still not clear to you? are your hearts so hard?

18 Having eyes, do you not see? and having ears, have you no hearing? and have you no memory?