Backbiting is a sin against Allah and also a wrong against a fellow servant, so repentance begins with the ordinary conditions: sincere regret, stopping the act, a firm resolve never to return to it, and turning back to Allah — "And turn to Allah in repentance, all of you, O believers, that you might succeed" (Quran 24:31). Beyond that, the Prophet (peace be upon him) said: "Whoever has wronged his brother in his honour or in anything else, let him seek his pardon today, before there comes a day when there is no dinar and no dirham" (Sahih al-Bukhari 2449). Scholars differ on whether the person must actually be told. Many hold that his pardon must be sought as with any other wrong done to a person. Others — including Shaykh al-Islam Ibn Taymiyyah and a group of the Salaf such as al-Hasan al-Basri — hold that if disclosing it would only create fresh enmity and hurt where none existed, it is enough to make du'a for him, seek Allah's forgiveness for him, and speak well of him in the same gatherings where he was disparaged, so that the harm caused is undone. Both positions are held by respected scholars; the second is what many advise today when informing the person would cause greater harm than good.
Q&A · Character
How does a person repent from backbiting — must I tell the person I backbit about them?
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.