Hilchos Rechilus, chapter 7, section 1

Rechilus is forbidden whether the speaker is a man or a woman, a relative or a stranger. Even if he heard someone say insulting things about his father and mother and told them about it, this is also rechilus. It also makes no difference whether the person the rechilus is about is a man or a woman, a child or an adult.

Some people stumble in this. A person sees two boys hitting each other, and goes to the father of one of them and tells him how so-and-so's son hit his son. Then that father hits the young boy who fought with his son, and a fight starts with the boy's father. Even if he knows for sure that the other boy was right in the fight, he may not tell unless all the conditions are met (they are brought in chapter 9).