Matthew 18:16

but if he do not listen, take with thee one or two more; that by the mouth of two or three witnesses every word may be established.

2 Corinthians 13:1

This is the third time I am coming to you. In the mouth of two or three witnesses shall every word be established.

John 8:17

Moreover, it is written in your law, that the witness of two men is true.

1 Timothy 5:19

Against an elder receive not an accusation without two or three witnesses.

Hebrews 10:28

He that hath set at nought the law of Moses dieth without mercy under two or three witnesses;

Matthew 26:60-61

and they found none, though many false witnesses came forward. But at last came two,

Revelation 11:3-7

And I will give power 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 do not listen, take with thee one or two more; that by the mouth of two or three witnesses every word may be established.
Matthew 26:60
and they found none, though many false witnesses came forward. But at last came two,
John 8:17
Moreover, it is written in your law, that the witness of two men is true.
2 Corinthians 13:1
This is the third time I am coming to you. In the mouth of two or three witnesses shall every word be established.
1 Timothy 5:19
Against an elder receive not an accusation without two or three witnesses.
Hebrews 10:28
He that hath set at nought the law of Moses dieth without mercy under two or three witnesses;
Revelation 11:3
And I will give power 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 judge a man, unless it first hear from him, and know what he doeth?