If a solitary witness testifies against someone before a Bais Din (Jewish Court) in a nonfinancial matter, violates this prohibition besides being guilty of speaking Lashon-Hora/Evil Speech. In financial matters the testimony of a single witness as practical effects. (It can obligate someone to make an oath.) In nonfinancial matters, however the Bais Din cannot accept the testimony of only one witness. Therefore coming to testify merely blackens the reputation of the person he speaks against without any beneficial results.
