DEUT956 "One witness shall not rise up against a man for any inquiry or for any sin" If a solitary witness testifies against someone before a Bais Din in a non-financial matter, he violates this prohibition besides being guilty of speaking loshon hora. In financial matters the testimony of a single witness has practical effects. (It can obligate someone to make an oath.) In non-financial matters, however, the Bais Din cannot accept the testimony of only one witness. Therefore his coming to testify merely blackens the reputation of the person he speaks against without any beneficial results.