It is very bad to destroy people's relationships with each other and one means to do so is gossiping. Gossiping is telling someone about someone else's private remarks with the goal of disrupting the relationship between the two people.
The Holy Quran refers to this behavior and orders the Holy Prophet (PBUH) to avoid paying attention to such remarks:
“Do not yield to one persistent in swearing, back-biting and gossiping.” (Verses 10-11 of Surah Al-Qalam)
Referring to the act of gossiping along with other big sins shows how grave it is. People who commit this sin are the ones who go from one person to another and make them mistrust each other and sow the seeds of enmity among them, which is among the gravest sins.
An educational point in this verse is that no one should trust people who are used to gossiping. Such persons should be rejected in the society.
If the two sides of an argument listen and pay attention to what a gossiper says, they are most likely to regret it.