Is money earned after remaining silent during someone's backbiting considered permissible?

Money earned from lawful work is considered lawful, and it has no relation to backbiting having occurred in the presence of the questioner. He should have objected to the one who backbit, or withdrawn from the gathering, for the Prophet, peace and blessings be upon him, said: "Whoever defends the honor of his brother, Allah will defend his face from the Hellfire on the Day of Resurrection." Now he must repent and seek forgiveness.