Luke 24:25
And he said, O foolish men! how slow you are to give belief to what the prophets have said.
Mark 7:18
And he said to them, Have even you so little wisdom? Do you not see that whatever goes into a man from outside is not able to make him unclean,
Mark 8:17-18
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?
Mark 9:19
And he said to them in answer, O generation without faith, how long will I have to be with you? how long will I put up with you? let him come to me.
Mark 16:14
And later he was seen by the eleven themselves while they were taking food; and he said sharp words to them because they had no faith and their hearts were hard, and because they had no belief in those who had seen him after he had come back from the dead.
Hebrews 5:11-12
Of whom we have much to say which it is hard to make clear, because you are slow of hearing.