Deuteronomy 19:15

One witness shall not be valid against a man for any iniquity or for any sin, in any sin which he should commit. At the mouth of two witnesses or at the mouth of three witnesses, shall the matter be established.

Numbers 35:30

Whoever kills any person, the murderer shall be put to death by the mouth of witnesses, but one witness shall not testify against any person to cause him to die.

Matthew 18:16

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

2 Corinthians 13:1

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

Deuteronomy 17:6

At the mouth of two witnesses or three witnesses shall he that is worthy of death be put to death, but at the mouth of one witness he shall not be put to death.

John 8:17

It is also written in your law that the testimony of two men is true.

1 Timothy 5:19

Against an elder do not receive an accusation, unless there are two or three witnesses.

Hebrews 10:28

He that despised the law of Moses died without mercy under two or three witnesses:

1 Kings 21:10

and set two men, sons of Belial, before him, to bear witness against him, saying, Thou didst blaspheme God and the king. And then carry him out and stone him that he may die.

1 Kings 21:13

Then the two men, sons of Belial, came in and sat before him; and those men of Belial witnessed against Naboth, in the presence of the people, saying, Naboth blasphemed God and the king. Then they carried him forth out of the city, and stoned him with stones that he died.

Matthew 26:60-61

but found none; though many false witnesses came, yet found they none. At the last came two false witnesses

Revelation 11:3-7

And I will give 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.

Bible References

At the mouth

Deuteronomy 17:6
At the mouth of two witnesses or three witnesses shall he that is worthy of death be put to death, but at the mouth of one witness he shall not be put to death.
Numbers 35:30
Whoever kills any person, the murderer shall be put to death by the mouth of witnesses, but one witness shall not testify against any person to cause him to die.
1 Kings 21:10
and set two men, sons of Belial, before him, to bear witness against him, saying, Thou didst blaspheme God and the king. And then carry him out and stone him that he may die.
Matthew 18:16
But if he will not hear thee, then take with thee one or two more that in the mouth of two or three witnesses every word may be established.
Matthew 26:60
but found none; though many false witnesses came, yet found they none. At the last came two false witnesses
John 8:17
It is also written in your law that the testimony of two men is true.
2 Corinthians 13:1
This third time I am coming unto you. In the mouth of two or three witnesses shall every word be established.
1 Timothy 5:19
Against an elder do not receive an accusation, unless there are two or three witnesses.
Hebrews 10:28
He that despised the law of Moses died without mercy under two or three witnesses:
Revelation 11:3
And I will give my two witnesses, and they shall prophesy a thousand two hundred and sixty days, clothed in sackcloth.

General references

Numbers 35:30
Whoever kills any person, the murderer shall be put to death by the mouth of witnesses, but one witness shall not testify against any person to cause him to die.
Deuteronomy 17:6
At the mouth of two witnesses or three witnesses shall he that is worthy of death be put to death, but at the mouth of one witness he shall not be put to death.
John 7:51
Does our law judge any man before it hears him and knows what he does?