"{And it is not for a believer}" means: it does not behoove a believer {to kill a believer except by mistake}, meaning unless he does not intend his killing. {And whoever kills a believer by mistake, then the freeing of a believing slave and a compensation (diya) delivered to his family}, meaning: the family of the slain, {unless they remit [it]}, meaning: unless the family of the slain remit it; thus they forgo the compensation. {But if he was from a people who are at war with you and he is a believer}, Al-Hasan said: A man would embrace Islam while his people were at war [with the Muslims], and a man from the Muslims would kill him by mistake—so for that there is the freeing of a believing slave [and no compensation] for his people. {And if he was from a people between whom and you is a covenant, then a compensation delivered to his family and the freeing of a believing slave}, regarding whatever covenant existed between the Muslims and the polytheists, or the People of the Covenant (Ahl al-Dhimma); if one of them was killed, then for that there is the compensation for his guardians, and the manumission of a believing slave. {And whoever does not find [the means], then a fast of two consecutive months, as a repentance from Allah}, meaning as a pardon from Allah.

Muhammad said: {A repentance from Allah}, the reading is with the fatha; the meaning: Allah ordained that as a repentance from Him.