Hilchos Rechilus, chapter 8, section 1

Many more things are forbidden because they are "avak rechilus" (the dust of rechilus). I will explain a few cases briefly, and a wise person will understand the law in similar cases.

For example: someone tells his friend how a certain person was asked about him, and that person answered, "Be quiet, I don't want to say what happened with him" — and other cases like this. That person's words hint something bad about him, since he does not want to say what is going on with him. This is avak rechilus.