Assalamu alaikum. I happen to backbite someone without knowing that he is actually a Muslim. I live in a kaffir country. What's the ruling for that? Am I sinful? Will I be held accountable?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If the mentioned person is personally unknown to you and to those you backbit him in their presence, be he is a Muslim or a non-Muslim, then this is not a forbidden backbiting, according to the view of Muslim scholars. However, a Muslim should guard his tongue against useless speech based on Prophetic guidance in the Hadith of the Prophet “He who believes in Allah and the Last Day must either speak good or remain silent.” [Agreed upon] For more information, kindly see Fatwa 227230 in the Arabic section.

Allah knows the best.