Luke 12:10

and every one whoever shall say a word to the Son of Man, it shall be forgiven to him, but to him who to the Holy Spirit did speak evil, it shall not be forgiven.

Matthew 12:31-32

Because of this I say to you, all sin and evil speaking shall be forgiven to men, but the evil speaking of the Spirit shall not be forgiven to men.

1 John 5:16

If any one may see his brother sinning a sin not unto death, he shall ask, and He shall give to him life to those sinning not unto death; there is sin to death, not concerning it do I speak that he may beseech;

1 Timothy 1:13

who before was speaking evil, and persecuting, and insulting, but I found kindness, because, being ignorant, I did it in unbelief,

Mark 3:28-30

'Verily I say to you, that all the sins shall be forgiven to the sons of men, and evil speakings with which they might speak evil,

Luke 23:34

And Jesus said, 'Father, forgive them, for they have not known what they do;' and parting his garments they cast a lot.

Hebrews 6:4-8

for it is impossible for those once enlightened, having tasted also of the heavenly gift, and partakers having became of the Holy Spirit,

Hebrews 10:26-31

For we -- wilfully sinning after the receiving the full knowledge of the truth -- no more for sins doth there remain a sacrifice,

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 have not known what they do;' and parting his garments they cast a lot.
Matthew 12:31
Because of this I say to you, all sin and evil speaking shall be forgiven to men, but the evil speaking of the Spirit shall not be forgiven to men.
Mark 3:28
'Verily I say to you, that all the sins shall be forgiven to the sons of men, and evil speakings with which they might speak evil,
1 Timothy 1:13
who before was speaking evil, and persecuting, and insulting, but I found kindness, because, being ignorant, I did it in unbelief,
Hebrews 6:4
for it is impossible for those once enlightened, having tasted also of the heavenly gift, and partakers having became of the Holy Spirit,
Hebrews 10:26
For we -- wilfully sinning after the receiving the full knowledge of the truth -- no more for sins doth there remain a sacrifice,
1 John 5:16
If any one may see his brother sinning a sin not unto death, he shall ask, and He shall give to him life to those sinning not unto death; there is sin to death, not concerning it do I speak that he may beseech;