Numbers 35:30
“‘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.
World English Bible (Public Domain)
In context
Before · Numbers 35:28–29
28because he should have remained in his city of refuge until the death of the high priest. But after the death of the high priest, the man slayer shall return into the land of his possession. 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.