Hilchos Lashon Hara chapter 6, section 1

It is forbidden to accept lashon hara, whether it is about a sin between a person and Hashem or between a person and other people. This means we may not believe in our hearts that the story is true, because that makes the person look bad in our eyes. This is forbidden even if the listener does not say out loud that he agrees. If he does say out loud that he agrees, he counts as both a speaker and a listener.

The listener breaks the negative commandment "Do not accept a false report." Chazal (our Sages) said this verse is a warning to the one who accepts lashon hara. This is in addition to the other commandments listed in the introduction.

Chazal also said that whoever speaks lashon hara deserves to be thrown to the dogs. This is because next to "Do not accept a false report" comes the verse "You shall throw it to the dogs." They also said that the one who accepts lashon hara is punished more than the one who says it.