Matthew 18:16

But if he does 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

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

1 Timothy 5:19

Against an elder receive not an accusation, except by two or three witnesses.

Hebrews 10:28

Any one who despised the law of Moses died without mercy by two or three witnesses;

John 8:17-18

And it is written also in your law, that the testimony 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

Matthew 18:16
But if he does not hear you, take with you one or two more, that by the mouth of two or three witnesses every word may be established;
John 8:17
And it is written also in your law, 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 word be established.
1 Timothy 5:19
Against an elder receive not an accusation, except by two or three witnesses.
Hebrews 10:28
Any one who despised the law of Moses died without mercy by two or three witnesses;