Hadith

1523. Abu Hurairah (May Allah be pleased with him) said: The Messenger of Allah (PBUH) said, "Do you know what is backbiting?'' The Companions said: "Allah and His Messenger know better.'' Thereupon he said, "Backbiting is talking about your (Muslim) brother in a manner which he dislikes.'' It was said to him: "What if my (Muslim) brother is as I say.'' He said, "If he is actually as you say, then that is backbiting; but if that is not in him, that is slandering.''
[Muslim].

Commentary:  This Hadith elaborates the meaning of backbiting and calumny and points out the difference between the two along with the evils of each one of them. Both these evils are mischief of the tongue and entail great troubles. May Allah save us from both.

1526. Anas (May Allah be pleased with him) said: The Messenger of Allah (PBUH) said, "During the Mi`raj (the Night of Ascension), I saw a group of people who were scratching their chests and faces with their copper nails. I asked, `Who are these people, O Jibril?' Jibril replied: `These are the people who ate flesh of others (by backbiting) and trampled people's honor.'''
[Abu Dawud].

Commentary:  "These are the people who ate flesh of others'' is a metaphor for backbiting. "To trample people's honor'' is akin to harming their goodwill and honor. The punishment for these things mentioned in Hadith makes their seriousness obvious.
--------------------