Backbiting Muslims is a major sin in Islam. It is not befitting a Muslim to backbite non Muslims and it is unethical. A Muslim is instructed to refrain from such acts even with non Muslims unless there is a need for that. Backbiting is allowed when it is to warn someone of another, to seek advice in a situation or to complain to the authorities. Muslims may gain sins by backbiting non Muslims but their good deeds wouldn’t go to them.