Deuteronomy 19:15
One witness shall not rise up against a man for any iniquity, or for any sin, in any sin that he sinneth: at the mouth of two witnesses, or at the mouth of three witnesses, shall the matter be established.
One witness shall not rise up against a man for any iniquity, or for any sin, in any sin that he sinneth,.... Whether capital sins, or pecuniary debts; or whatsoever sins a man may be guilty of whether sins against the first or second table of the law, whether greater or lesser sins, whether in moral or civil things; the Jews except only in the case of a woman suspected of adultery and of beheading the heifer:
at the mouth of two witnesses, or at the mouth of three witnesses, shall the matter be established; either for acquittance or condemnation; and the witnesses may not, as Jarchi says, write their testimony in a letter, and send it to the sanhedrim, nor may an interpreter stand between the witnesses and the judges;
See Gill on "Deuteronomy 17:6".