Shemiras Halashon Halachos

Hilchos Lashon Hara chapter 8, section 1

This chapter will go into more details concerning the prohibition of speaking and listening to lashon hara. 1. The prohibition applies to man, woman, relative or non-relative. Even though a person is generally does not mind when a relative speaks lashon hara about him, and even though a person generally does not intend to disparage his relative but rather, is upset at a perceived wrong-doing of the relative, nonetheless, if he hurriedly judged the relative harshly and he actually did not do a wrongdoing, this is absolute lashon hara.

Hilchos Lashon Hara chapter 8, section 2

Whom does the Torah forbid speaking lashon hara of? It applies to man and woman, whether one's own wife or another woman. Many people think it is permitted to speak of a wife or in-laws to brothers or relatives. Actually, there is no such distinction unless one's intent is for a future benefit and not to disparage them. Also, no falsehood should be included in what one says. The rules explained later in chapter 10 (paragraph 13 onwards) all apply here.