Do not gossip or listen to gossip (lashon hara). This is one of the biggest mitzvot. You are not to gossip, insult, lie, deceive, or slander. When you listen to gossip, your fellow man is brought down. This can be so serious that when you insult someone in public and he blushes, you are considered to have killed a part of that person's soul.

Brenda Shoshanna, Jewish Dharma