Assalamu Alaikum wa Rahmatallahi wa Barakatuhu
If one backbit somebody else, is it necessary to ask that person for forgiveness if they did not know? Or are we supposed to repent without telling the person that they were backbitten?
Jazakum allahu khair
fi aman allah
w'salaam
It is Huququl Ibaad. Rights of the Servants of allah, that you go to them and ask for forgiveness. Backbiting is when you say something behind someone's back, so by definition, the person would not know what you are saying.
It's related in Hadith, I believe it's in Sunan Abi Dawud, but correct me if I am mistaken, "Gatherings are with trust."
There are various types of gatherings. Those that were to the public and those that were private. Private would consist of family meetings, etc. You won't ask the newspapers and media to televise the private family meeting.
You are to keep everything that went on in that gathering in private. That means what actions, reactions, what was written, and what was said all must be in private, unless you have EVERYONE'S (not even ONE objection) permission to say what went on behind those closed doors.
Just by even saying "That person came happily" or "that person came reluctantly" is a form of gheebat, because you might be alluding towards something that went on in the gathering or what the gathering content was.