Hilchos Lashon Hara chapter 10, section 16

All this indicates what a mistake people make. If one asks someone why he spoke lashon hara about someone else he replies, “Because he spoke about me to so and so.” This is a mistake. First, if one heard of his speaking about oneself from the person he spoke to, one may not believe him because it forbidden to believe lashon hara. Also, even if it is true, it is still forbidden to speak about him as we said in paragraph 11.