What is the ruling on backbiting a Muslim or ridiculing him in front of a disbeliever or an apostate, or laughing when he is insulted, with no intention of showing loyalty or assisting against him, and when is that considered aiding a disbeliever against a Muslim or an act of disbelief?

Listening to thegheebah (backbiting) or mockery of a disbeliever is forbidden, just as it is forbidden to listen to it from a Muslim. It is not permissible to approve of it or laugh at it, because the listener and participant in backbiting incurs sin. This prohibition is based on the prohibition of backbiting and mockery in Islam, as established by Quranic texts. As for showing loyalty to disbelievers, taking them as allies, befriending them, and loving them, this is forbidden because it contradicts the doctrine of al-wala' wal-bara' (loyalty and disavowal). Furthermore, assisting them against Muslims is considered an act of disbelief. However, merely laughing at the words of a disbeliever or listening to his backbiting or mockery is not in itself an act of disbelief, even though it is forbidden.