L'Fum Tzaara Agra:

Sefer Divrei Yisroel (Klalei Ohraysa, Ois 30) states the following explanation of the Mishnah (Avos 5:23): “L'fum tzaarah agra” (one is rewarded in accordance to the pain): The word "l'fum” can be translated to mean “the mouth”. Thus, the Mishnah is saying that the mouth can cause “tzaarah or agra". It can cause pain through speaking lashon hara, or it can create reward through words of Torah.