What is the way to repent from backbiting a Christian man and thinking ill of him, considering the difficulty of informing him or informing those in front of whom he was backbitten, and is remorse, ceasing backbiting, and praising him in front of others sufficient?

Backbiting is forbidden regarding a Muslim and a non-belligerent disbeliever. It is by Allah's grace that He has opened the door to repentance from backbiting and other sins. One must hasten to sincere repentance, along with seeking absolution from the one who was backbitten: if he knew about the backbiting, then he must be informed of what happened, but if he did not know, then it is preferable to seek general absolution without mentioning the backbiting, while frequently supplicating for his guidance and praising him.