陰口蔭影 Kanji
だれか人に、言い分があったら、陰口をいわないで、その人に面と向かっていいなさい。 If you have a bone to pick with a person, tell it to his face instead of saying things behind his back.
陰口叩 Kanji
他人の陰口をたたくな。 Don't speak ill of others behind their back.