Hafetz Haim Halachot
Halacha 34 / 215

Hilchos Lashon Hara, Opening – positive commands (10)

Whoever speaks lashon hara about his oldest brother, his mother's husband, or his father's wife also breaks the positive commandment (Shemos 20:12), "Honor your father and your mother." From the extra word "es" in the verse, we learn that these people must be honored too.

All the more so, Heaven forbid, speaking lashon hara about one's own father or mother surely breaks the positive mitzvah of honoring parents. Besides this, he also breaks (Devarim 27:16), "Cursed be he who denigrates his father or mother."