Deuteronomy 19:15

15 A single witness shall not suffice to convict a person of any crime or wrongdoing in connection with any offense that may be committed. Only on the evidence of two or three witnesses shall a charge be sustained.

Deuteronomy 19:15 In-Context

13 Show no pity; you shall purge the guilt of innocent blood from Israel, so that it may go well with you.
14 You must not move your neighbor's boundary marker, set up by former generations, on the property that will be allotted to you in the land that the Lord your God is giving you to possess.
15 A single witness shall not suffice to convict a person of any crime or wrongdoing in connection with any offense that may be committed. Only on the evidence of two or three witnesses shall a charge be sustained.
16 If a malicious witness comes forward to accuse someone of wrongdoing,
17 then both parties to the dispute shall appear before the Lord, before the priests and the judges who are in office in those days,
New Revised Standard Version Bible, copyright 1989, Division of Christian Education of the National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved.