Numbers 35:30
TSK
"'Whoever kills any person, the murderer shall be slain at the mouth of witnesses: but one witness shall not testify against any person that he die.
TSK
Treasury of Scripture Knowledge references in WEB.
"'Whoever kills any person, the murderer shall be slain at the mouth of witnesses: but one witness shall not testify against any person that he die.
One witness shall not rise up against a man for any iniquity, or for any sin, in any sin that he sins: at the mouth of two witnesses, or at the mouth of three witnesses, shall a matter be established.
It's also written in your law that the testimony of two people is valid.
Don't receive an accusation against an elder, except at the word of two or three witnesses.
For there are three who testify: