Matthew 18:16

But if he will not hear thee, take with thee one or two more, that by the mouth of two or three witnesses every word may be confirmed.

2 Corinthians 13:1

THIS third time I am coming to you: by the mouth of two or three witnesses shall every charge be established.

John 8:17

Now even in your law it is written, that the testimony of two men is true.

1 Timothy 5:19

Against a presbyter receive not an accusation, except it be from two or three witnesses.

Hebrews 10:28

Any man who treated the law of Moses with neglect, was put to death, without mercy, on the deposition of two or three witnesses:

Matthew 26:60-61

and found none: and though many false witnesses came, they found it not [sufficient]. But at the last two false witnesses stepping forth,

Revelation 11:3-7

And I will give charge to my two witnesses, and they shall prophesy a thousand two hundred and sixty days, clothed in sackcloth.

Treasury of Scripture Knowledge

Summary

One witness shall not rise up against a man for any iniquity, or for any sin, in any sin that he sinneth: at the mouth of two witnesses, or at the mouth of three witnesses, shall the matter be established.

General references

Bible References

At the mouth

Matthew 18:16
But if he will not hear thee, take with thee one or two more, that by the mouth of two or three witnesses every word may be confirmed.
Matthew 26:60
and found none: and though many false witnesses came, they found it not [sufficient]. But at the last two false witnesses stepping forth,
John 8:17
Now even in your law it is written, that the testimony of two men is true.
2 Corinthians 13:1
THIS third time I am coming to you: by the mouth of two or three witnesses shall every charge be established.
1 Timothy 5:19
Against a presbyter receive not an accusation, except it be from two or three witnesses.
Hebrews 10:28
Any man who treated the law of Moses with neglect, was put to death, without mercy, on the deposition of two or three witnesses:
Revelation 11:3
And I will give charge to my two witnesses, and they shall prophesy a thousand two hundred and sixty days, clothed in sackcloth.

General references

John 7:51
Doth our law condemn a man, without first hearing his defence, and knowing what he hath done?