Allah subhana WA ta'ala made it clear that defaming another Muslim in his/her absence is like eating the flesh of one’s dead brother (49:12), which obviously, everybody hates. Hence, it is the most dreadful sin. Note that if the person is present, he/she may have a chance to defend himself/herself, although everybody does not have the courage to defend themselves in these circumstances. If, however, he/she is defamed in his/her absence, the damage is deep and somewhat permanent.
The tongue alone does not do backbiting; it can also be done with the eyes, hands and other movements. For example, imitating somebody who is limping, in order to insult him/her.
Muhammad sallallahu allahi WA salam said: ” Backbiting is a worse sin than adultery.” It is further explained in a saying of the Prophet sallallahu allayi WA salam, narrated by Abu Sa’eed and Jubair in Bayhaqi: “Allah may forgive a person if he/she repents after committing adultery. However, Allah will not forgive the one who backbites, till his/her victim forgives him/her.”
One time, the Messenger of Allah sallallahu allahi WA salam pointed towards two graves and said to his companions that both of these people are being punished in their graves. One of them used to backbite people and the other was not careful about spilling drops of urine of his clothes and body whilst urinating.
The Prophet sallallahu allahi WA salam during his Me’raj journey saw some people who had nails made of red copper. They were tearing apart their faces and chests with these nails. The Noble Prophet sallallahu allahi WA salam asked the Angel Jibrail (AS) about them, He said, “They are being punished because they used to eat people’s flesh in their lives, i.e. used to backbite and defame others.
Abu Hurayra (RA) narrates that the Noble Prophet sallallahu allahi WA salam said, “The killing of a Muslim by another unjustly, usurping others’ wealth or defaming other Muslims is totally forbidden (or Haram).” (Sahih Muslim)
Insha Allah thus helps you !