Allah, the Exalted, says:

"A slanderer, going about with calumnies.'' (68:11)

"Not a word does he (or she) utter, but there is a watcher by him ready (to record it).'' (50:18)

Hudhaifah (radiallahu anh) said: The Messenger of Allah (salallahu alayhi wasallam) said, "The person who goes about with calumnies (false and malicious statements) will never enter Jannah.''
[Al-Bukhari and Muslim]

Ibn `Abbas (radiallahu anhuma) said: The Messenger of Allah (salallahu alayhi wasallam) passed by two graves and said, "Both of them (the persons in these graves) are being tortured, and they are not being tortured for a cardinal sin. But indeed they are great sins. One of them used not to save himself from being soiled with his urine, and the other one used to go about with calumnies (among the people to rouse hostilities, e.g., one goes to a person and tells him that so-and-so says about him such and such evil things).''
[Al-Bukhari and Muslim]

Talebearing (a person who spreads gossip, secrets, etc., that may cause trouble or harm), carelessness in saving oneself from splash of urine drops, and lack of observance of privacy are sins which are liable to punishment.
The Hadith also proves punishment in the grave.

Ibn Mas`ud (radiallahu anh) said: The Prophet (salallahu alayhi wasallam) said, "Shall I tell you what `Al-`Adhu' (falsehood and slandering) is? It is calumny which is committed among the people.''
[Muslim]

We learn from this Hadith that calumny, lying, falsehood and slandering are major sins because they cause conflict and dissension in society. A Muslim must keep himself free from such evils.