Matthew 18:16

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

2 Corinthians 13:1

The third time am I coming to you. By the mouth of two or three witnesses, every matter shall be established.

John 8:17

It is also written in your law, The testimony of two is worthy of credit.

1 Timothy 5:19

Receive not an accusation against an old man, unless before two or three witnesses.

Hebrews 10:28

He that despised Moses law, died without mercy, on the testimony of two or three witnesses:

Matthew 26:60-61

and found none. Though many false witnesses came, yet they found none. At last two false witnesses came,

Revelation 11:3-7

And I will give to my two witnesses, that they may 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 you, take with you one or two more, that, by the mouth of two or three witnesses, every word may be established.
Matthew 26:60
and found none. Though many false witnesses came, yet they found none. At last two false witnesses came,
John 8:17
It is also written in your law, The testimony of two is worthy of credit.
2 Corinthians 13:1
The third time am I coming to you. By the mouth of two or three witnesses, every matter shall be established.
1 Timothy 5:19
Receive not an accusation against an old man, unless before two or three witnesses.
Hebrews 10:28
He that despised Moses law, died without mercy, on the testimony of two or three witnesses:
Revelation 11:3
And I will give to my two witnesses, that they may prophesy a thousand two hundred and sixty days, clothed in sackcloth.

General references

John 7:51
Does our law condemn a man unless it first hear from him, and know what he does?