Will it be Wajib (obligatory) for a Muslim to make a Kaffarah (expiation) if they commit a manslaughter of a Christian?
a Muslim commits a manslaughter of a Musta'man (non-Muslim with a peace agreement permitting them to enter and stay temporarily in a Muslim country), for instance in a car accident; it will be Wajib on the Muslim to make a Kaffarah for such a doing. A proof for the foregoing is the Ayah (Qur'anic verse) in which Allah (Exalted be He) says:
...and if he belonged to a people with whom you have a treaty of mutual alliance, compensation (blood-money - Diya) must be paid to his family, and a believing slave must be freed. And whoso finds this (the penance of freeing a slave) beyond his means, he must fast for two consecutive months in order to seek repentance from Allâh. And Allâh is Ever All-Knowing, All-Wise.
(Part No. 21; Page No. 346) It is also because such a Christian, who has been killed wrongly, is a human being whose soul has to be preserved just as the case with Muslims.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.