Shemiras Halashon Halachos

Hilchos Rechilus, chapter 3, section 2

It is rechilus to say to anyone that Reuven spoke against Shimon, because the story will spread and will cause enmity between Reuven and Shimon. Even if one warns the person one speaks to not to spread the story, and even if one knows for sure that he will not spread the story, it is still forbidden, because merely saying that Reuven spoke against Shimon is itself generally lashon hora.

Hilchos Rechilus, chapter 3, section 3 4

How much more is it forbidden to say that someone spoke against his sons or relatives, for the sons and relatives will naturally be extremely upset if they hear of it. If one tells someone that Reuven spoke against Shimon so that the person one tells this to should rebuke Reuven for what he did, see laws of lashon hora paragraph 114.