Deuteronomy 17:6

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

Numbers 35:30

Whoso killeth any person, the murderer shall be slain at the mouth of witnesses: but one witness shall not testify against any person that he die.

Deuteronomy 19:15

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 a matter be established.

Matthew 18:16

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

2 Corinthians 13:1

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

1 Timothy 5:19

Against an elder receive not an accusation, except at the mouth of two or three witnesses.

Hebrews 10:28

A man that hath set at nought Moses law dieth without compassion on the word of two or three witnesses:

John 8:17-18

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

Treasury of Scripture Knowledge

Summary

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.

Bible References

General references

Deuteronomy 19:15
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 a matter be established.
Numbers 35:30
Whoso killeth any person, the murderer shall be slain at the mouth of witnesses: but one witness shall not testify against any person that he die.
Matthew 18:16
But if he hear thee not, take with thee one or two more, that at the mouth of two witnesses or three every word may be established.
John 8:17
Yea and in your law it is written, that the witness of two men is true.
2 Corinthians 13:1
This is the third time I am coming to you. At the mouth of two witnesses or three shall every word established.
1 Timothy 5:19
Against an elder receive not an accusation, except at the mouth of two or three witnesses.
Hebrews 10:28
A man that hath set at nought Moses law dieth without compassion on the word of two or three witnesses:

American Standard Version Public Domain