Numbers 35:30 in the King James Version
Whoso killeth any person, the murderer shall be put to death by the mouth of witnesses: but one witness shall not testify against any person to cause him to die.
Context
29 “‘These things shall be for a statute and ordinance to you throughout your generations in all your dwellings.
30 “‘Whoever kills any person, the murderer shall be slain based on the testimony of witnesses; but one witness shall not testify alone against any person so that he dies.
31 “‘Moreover you shall take no ransom for the life of a murderer who is guilty of death. He shall surely be put to death.