What is the ruling on someone who backbites others out of ignorance that backbiting is forbidden, and is he required to seek absolution from those he backbithed?

Backbiting is forbidden by text and consensus, based on Allah's saying: "And do not backbite each other. Would one of you like to eat the flesh of his brother when dead? You would detest it. And fear Allah. Indeed, Allah is Forgiving and Merciful." Whoever is ignorant of its prohibition is not sinful unless they were negligent and fell short in seeking knowledge. It is not obligatory to seek forgiveness from those one has backbitten; rather, one should supplicate for them and mention their good qualities, to avoid greater harms.