Deuteronomy 17:6-8

Young's Literal Translation

⁶ By the mouth of two witnesses or of three witnesses is he who is dead put to death; he is not put to death by the mouth of one witness;

⁷ the hand of the witnesses is on him, in the first place, to put him to death, and the hand of all the people last; and thou hast put away the evil thing out of thy midst.

⁸ `When anything is too hard for thee for judgment, between blood and blood, between plea and plea, and between stroke and stroke -- matters of strife within thy gates -- then thou hast risen, and gone up unto the place on which Jehovah thy God doth fix,