Deuteronomy 19:15

‘If anyone strikes down a person, the murderer shall be put to death at the mouth of witnesses, but no person shall be put to death on the testimony of one witness.

“On the mouth of two witnesses or three witnesses, he who is to die shall be put to death; he shall not be put to death on the mouth of one witness.

“Speak to the sons of Israel, saying, ‘Designate the cities of refuge, of which I spoke to you by the hand of Moses,

“But if he does not listen to you, take one or two more with you, so that by the mouth of two or three witnesses every fact may be confirmed.

And they did not find any, even though many false witnesses came forward. But later on two came forward,

“Does our Law judge a man unless it first hears from him and knows what he is doing?”

“Even in your law it has been written that the witness of two men is true.

This is the third time I am coming to you. By the mouth of two or three witnesses every matter shall be confirmed.

Do not receive an accusation against an elder except on the basis of two or three witnesses.

Anyone who has set aside the Law of Moses dies without mercy by the mouth of two or three witnesses.