Numbers 35:28-30

Young's Literal Translation

²⁸ for in the city of his refuge he doth dwell till the death of the chief priest; and after the death of the chief priest doth the man-slayer turn back unto the city of his possession.

²⁹ `And these things have been to you for a statute of judgment to your generations, in all your dwellings:

³⁰ whoso smiteth a person, by the mouth of witnesses doth [one] slay the murderer; and one witness doth not testify against a person -- to die.