Hilchos Lashon Hara chapter 7, section 9

If the person who told the lashon hara was mentioning it casually, without meaning to report (mesi'ach lefi tumo), this is the rule: If the matter can be judged favorably, or if the speaker did not see it himself but only heard it from others, it is certainly forbidden to accept it from him and decide that the person is to blame.

And all the more so, it is forbidden to go and tell others, or to cause him to lose money, or to hit him because of what he heard.