לישועת אלחנן בן הענא מרים
Someone who speaks against his fellow transgresses a negative command as it says (Vayikra 19:16), "Do not go as a talebearer (rachil) in your nation." What is a rachil? Someone who carries things and goes from this person to that saying, "Ploni said this about you, and I heard that ploni did that to you", even if it is true. This person is among those who destroy the world. There is a much worse sin than this, namely, lashon hara, which is included in this negative command. This is someone who speaks of the bad of his fellow even if the says the truth, but someone who say lies is considered a slanderer of his fellow.
Hilchos Lashon Hara, Opening – Negative commands (2)
The speaker or receiver also transgress the negative command (Shemos 23:1), "Do not accept (lo tisah) an empty statement," which can also be read as lo tasi (do not report), and thus, this negative command includes them both, the speaker and the receiver.
