Why Backbiting is considered a great sin?

Incentives of Backbiting

(1) Enmity and envy are the strongest incentives of backbiting.

(2) Joking is another incentive of backbiting, because it is regarded as fresh subject for arising joking and laughter at others.

(3) Boasting is also an incentive of backbiting, because the boastful, in most cases, tries to refer to the others’ defects to prove that he disdains and does not enjoy such defects.

(4) It frequently happens that an individual who associates with backbiters tries to be in conformity with them by according them in their ill speech of others so that they may not reject him.

Disadvantages of Backbiting

Through its regulations, Islam intends to reinforce fraternity of Muslims to make it a never-ending constitution. Thus, it has gone on enjoining to cling to all matters that develop mutual amicability and achieve fraternity; such as well mannerism, truth, fulfillment of trusts, and paying attention to Muslims’ affairs and general interests. Islam also has warned against any matter that roils the pure hearts or arises malice, such as lying, cheating, treachery, and contempt.

Since backbiting is a destructive element that devastates the social construction and spoils the tied up relations, the Islamic code has forbidden and regarded it as a grand sin. It sows the poisonous seeds of spite among Muslims. When the ill speech reaches the one about whom it is said, it will arise the feelings of hatred in his inner self; so, he tries to revenge himself upon the backbiter by answering him by ill speech. In so many cases, backbiting has caused serious problems and unwelcome tragedies.

The Prophet (PBUH&HH) said: “On the Day of Resurrection, one of you will not find the good deeds that he did in his life in his record¹ when he will be interrogated. He will ask the Lord about this, and the Lord will answer him: ‘Your Lord never makes a mistake and never forgets. Because you backbit people, your good deeds were erased from your record.’ Another one will find many good deeds that he did not do in his record. He will ask the Lord about such deeds, and the Lord will answer:
“Because you were backbitten by so-and-so, I added his good deeds to you.”²

1- ‘Record’, here, stands for the record of the good and bad deeds of every human being that will be shown to him on the Day of Resurrection and according to which he will be judged. In the holy Qur’an , there are indications to this record, such as in God’s saying: (On the day when We call every nation with their leaders, those whose record of deeds are given to their right hands will read the record and the least wrong will not be done to them. 17:71)
2- Quoted from Jami us-Saadat; part 2 page 301.

source:english.almaaref