Prophet Muhammed (S.A.W) said:

"Backbiting is worse than unlawful intercourse"

This Hadith continues with the Companions asking the Messenger of Allah (S.A.W) why backbiting is more severe.

Allah's Messenger (S.A.W) replied that the person who fornicates is forgiven by Allah if he sincerely repents but the one who backbites is not forgiven until the person he transgressed against forgives him.

Another reason for this is that unlawful intercourse is normally recognised by the fornicator as a serious sin; hence, there is a greater chance for him turning to Allah and repenting.

On the other hand a person who backbites does not normally realize the seriousness of his sin and takes it lightly; hence he does not stop and repent.

So please [FORGIVE ME for anything I may have said that may classify as backbiting.