All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Muslim scholars have different opinions concerning the expiation if a Muslim kills a non-Muslim accidentally whether he is a Thimmi (one who lives under the protection of an Islamic government and pays protection taxes) or an ally of Muslims. Majority of them are of the opinion that he has to pay the expiation, while some believe that there is no expiation due on him.
Imaam Ibn Qudaamah said: 'Expiation is due on the killing of an innocent non-Muslim whether he is a Thimmi or the one who has been granted temporary protection; this is the opinion of the majority of Muslim scholars. Imaams Al-Hassan and Maalik are of the opinion that there is no expiation due in this case… we based our opinion on the verse which means {… and if he was from a people with whom you have a treaty — then a compensation payment presented to his family and the freeing of a believing slave.}[Quran 4:92]. Furthermore, he is also a human killed unjustly, so the expiation of killing him is compulsory just as in the case of a Muslim.'
The opinion of the majority of Muslim scholars is safer and more appropriate to become free from the responsibility. Imaam Ibn Taymiyyah also preferred this opinion.
The expiation of accidental killing is freeing a slave: if one cannot then he has to fast for two months consecutively. If he is not able to fast then he has to feed sixty poor people according to some scholars, while some others say that feeding is not due on him. There is no evidence in the prophetic narrations that proves feeding.
For details read our Fatwa: 88305 about ruling of killing accidentally and Fatwa: 86122 about the blood money of a non-Muslim.
Allaah Knows best.