Deuteronomy 19:15; Numbers 35:30

Laws Concerning Witnesses

15 A single witness shall not suffice against a person for any crime or for any wrong in connection with any offense that he has committed. bOnly on the evidence of two witnesses or of three witnesses shall a charge be established.

30 If anyone kills a person, the murderer shall be put to death on the levidence of witnesses. But no person shall be put to death on the testimony of one witness.