Luke 12:10

And every one that speaks a word against the Son of man shall have forgiveness; but he that blasphemes against the Holy Spirit shall not be forgiven.

Matthew 12:31-32

Therefore, I tell you, every sin and blasphemy shall be forgiven men, but the blasphemy of the Spirit shall not be forgiven men.

1 John 5:16

If any one sees his brother commit a sin, not to death, he shall ask, and he will give him life, for those who sin not to death. There is a sin to death; I say not that you should pray for it.

1 Timothy 1:13

who formerly was a blasphemer and persecutor and an injurious man; but I obtained mercy because I did those things ignorantly in unbelief;

Mark 3:28-30

I tell you truly, That all sins and blasphemies with which they blaspheme shall be forgiven the children of men;

Luke 23:34

And Jesus said, Father, forgive them, for they know not what they do. And distributing his garments they cast lots [for them].

Hebrews 6:4-8

For those once enlightened and having tasted of the heavenly gift and been made partakers of the Holy Spirit,

Hebrews 10:26-31

For if we sin willingly after having received the knowledge of the truth, there is no longer a sacrifice left for sins,

Treasury of Scripture Knowledge

Summary

And whosoever shall speak a word against the Son of man, it shall be forgiven him: but unto him that blasphemeth against the Holy Ghost it shall not be forgiven.

Bible References

General references

Luke 23:34
And Jesus said, Father, forgive them, for they know not what they do. And distributing his garments they cast lots [for them].
Matthew 12:31
Therefore, I tell you, every sin and blasphemy shall be forgiven men, but the blasphemy of the Spirit shall not be forgiven men.
Mark 3:28
I tell you truly, That all sins and blasphemies with which they blaspheme shall be forgiven the children of men;
1 Timothy 1:13
who formerly was a blasphemer and persecutor and an injurious man; but I obtained mercy because I did those things ignorantly in unbelief;
Hebrews 6:4
For those once enlightened and having tasted of the heavenly gift and been made partakers of the Holy Spirit,
Hebrews 10:26
For if we sin willingly after having received the knowledge of the truth, there is no longer a sacrifice left for sins,
1 John 5:16
If any one sees his brother commit a sin, not to death, he shall ask, and he will give him life, for those who sin not to death. There is a sin to death; I say not that you should pray for it.