Prohibitions 1-3

1. לא תלך רכיל בעמיך (Vayikra 19:16): This negative mitzvah applies to both rechilus which is essentially tattle telling and lashon hara which is speaking bad about others even if it is the truth. This sin only applies to the one speaking. 

2. לא תשא שמע שוא (Shemos 23:1): According to most opinions applies to the one listening and accepting loshon hara or rechilus. It is based on the case of a judge not allowed to accept testimony before a court case officially begins even if it is exactly what he is going to be hearing in the court case. 

3. נשמר מאד מנגע הצרעת (Devarim 24:8): There is a prohibition on getting yourself to have tzaraas, a spiritual ailment in the times of the beis hamikdash and before, which one of its causes is lashon hara.