Mark 6:52

for they did not understand the lesson of the loaves; their minds were dull.

Mark 3:5

So Jesus looked around at them in anger, because He was pained over their stubbornness of mind, and said to the man, "Hold out your hand." And he held it out, and his hand was cured.

Mark 8:17-21

And as He noticed it He said to them, "Why are you discussing the fact that you have no bread? Do you not yet know nor understand? Are your minds so dull?

Matthew 16:9-11

Do you not understand yet? Do you not remember the five loaves for the five thousand and how many basketfuls you took up?

Mark 7:18

And He answered them, "Are you too without understanding yet? Do you not know that nothing from the outside that goes into a man can make him foul,

Mark 16:14

Later on He appeared to the Eleven themselves while they were at table, and reproved them for their lack of faith and their stubbornness, because they had not believed those who had seen Him after He had been raised from the dead.

Luke 24:25

Then He said to them, "O men sluggish in mind and slow in heart to believe all that the prophets have said!

Romans 11:7

What are we then to conclude? Israel has failed to obtain what it is still in search for, but His chosen ones have obtained it. The rest have become insensible to it,

Treasury of Scripture Knowledge

Summary

For they considered not the miracle of the loaves: for their heart was hardened.

General references

Bible References

They

Mark 7:18
And He answered them, "Are you too without understanding yet? Do you not know that nothing from the outside that goes into a man can make him foul,
Mark 8:17
And as He noticed it He said to them, "Why are you discussing the fact that you have no bread? Do you not yet know nor understand? Are your minds so dull?
Matthew 16:9
Do you not understand yet? Do you not remember the five loaves for the five thousand and how many basketfuls you took up?
Luke 24:25
Then He said to them, "O men sluggish in mind and slow in heart to believe all that the prophets have said!

Their

Mark 3:5
So Jesus looked around at them in anger, because He was pained over their stubbornness of mind, and said to the man, "Hold out your hand." And he held it out, and his hand was cured.
Mark 16:14
Later on He appeared to the Eleven themselves while they were at table, and reproved them for their lack of faith and their stubbornness, because they had not believed those who had seen Him after He had been raised from the dead.

General references

Matthew 15:16
And He said, "Are you too, even yet, without understanding?