Matthew 18:16

But if he does not listen [to your reasoning], take one or two other people with you, so that two or three witnesses can verify every word [that was said].

John 8:17

Even in your law it is written [Deut. 19:15] that the testimony of two people is true.

2 Corinthians 13:1

This will be my third visit to you. [Deut. 19:15 says], "Every matter should be settled by the testimony of two or three witnesses."

1 Timothy 5:19

Do not listen to an accusation against an elder unless it comes from two or three witnesses.

Hebrews 10:28

The person who has disregarded the law of Moses is put to death without being shown mercy on the testimony of two or three witnesses.

1 John 5:7-8

For there are three who give their testimony [about Jesus]:

Revelation 11:3

And I will give [authority] to my two witnesses and they will prophesy for 1,260 days, wearing sackcloth" [i.e., a black, coarse cloth made of goat's hair].

Treasury of Scripture Knowledge

Summary

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.

Bible References

That in

John 8:17
Even in your law it is written [Deut. 19:15] that the testimony of two people is true.
2 Corinthians 13:1
This will be my third visit to you. [Deut. 19:15 says], "Every matter should be settled by the testimony of two or three witnesses."
1 Timothy 5:19
Do not listen to an accusation against an elder unless it comes from two or three witnesses.
Hebrews 10:28
The person who has disregarded the law of Moses is put to death without being shown mercy on the testimony of two or three witnesses.
1 John 5:7
For there are three who give their testimony [about Jesus]:
Revelation 11:3
And I will give [authority] to my two witnesses and they will prophesy for 1,260 days, wearing sackcloth" [i.e., a black, coarse cloth made of goat's hair].