Matthew 17:20

And Jesus said to them, 'Through your want of faith; for verily I say to you, if ye may have faith as a grain of mustard, ye shall say to this mount, Remove hence to yonder place, and it shall remove, and nothing shall be impossible to you,

Luke 17:6

and the Lord said, 'If ye had faith as a grain of mustard, ye would have said to this sycamine, Be uprooted, and be planted in the sea, and it would have obeyed you.

Matthew 13:31

Another simile he set before them, saying: 'The reign of the heavens is like to a grain of mustard, which a man having taken, did sow in his field,

Matthew 21:21

And Jesus answering said to them, 'Verily I say to you, If ye may have faith, and may not doubt, not only this of the fig-tree shall ye do, but even if to this mount ye may say, Be lifted up and be cast into the sea, it shall come to pass;

Mark 11:23

for verily I say to you, that whoever may say to this mount, Be taken up, and be cast into the sea, and may not doubt in his heart, but may believe that the things that he saith do come to pass, it shall be to him whatever he may say.

1 Corinthians 13:2

and if I have prophecy, and know all the secrets, and all the knowledge, and if I have all the faith, so as to remove mountains, and have not love, I am nothing;

Mark 9:23

And Jesus said to him, 'If thou art able to believe! all things are possible to the one that is believing;'

Matthew 14:30-31

but seeing the wind vehement, he was afraid, and having begun to sink, he cried out, saying, 'Sir, save me.'

Matthew 17:9

And as they are coming down from the mount, Jesus charged them, saying, 'Say to no one the vision, till the Son of Man out of the dead may rise.'

Matthew 17:17

And Jesus answering said, 'O generation, unstedfast and perverse, till when shall I be with you? till when shall I bear you? bring him to me hither;'

Mark 4:31

As a grain of mustard, which, whenever it may be sown on the earth, is less than any of the seeds that are on the earth;

Luke 1:37

because nothing shall be impossible with God.'

Luke 18:27

and he said, 'The things impossible with men are possible with God.'

John 11:40

Jesus saith to her, 'Said I not to thee, that if thou mayest believe, thou shalt see the glory of God?'

1 Corinthians 12:9

and to another faith in the same Spirit, and to another gifts of healings in the same Spirit;

Hebrews 3:19

and we see that they were not able to enter in because of unbelief.

Treasury of Scripture Knowledge

Summary

And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.

Bible References

Because

Matthew 17:17
And Jesus answering said, 'O generation, unstedfast and perverse, till when shall I be with you? till when shall I bear you? bring him to me hither;'
Matthew 14:30
but seeing the wind vehement, he was afraid, and having begun to sink, he cried out, saying, 'Sir, save me.'
Hebrews 3:19
and we see that they were not able to enter in because of unbelief.

A grain

Matthew 13:31
Another simile he set before them, saying: 'The reign of the heavens is like to a grain of mustard, which a man having taken, did sow in his field,
Mark 4:31
As a grain of mustard, which, whenever it may be sown on the earth, is less than any of the seeds that are on the earth;

Nothing

Mark 9:23
And Jesus said to him, 'If thou art able to believe! all things are possible to the one that is believing;'
Luke 1:37
because nothing shall be impossible with God.'
Luke 18:27
and he said, 'The things impossible with men are possible with God.'