What are the conditions concerning the status of the victim for retribution to be mandatory?

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For retribution to be mandatory, the slain person must be a free Muslim (Hurr Muslim), equivalent in status to the killer. If the killer is a free Muslim, it is required that the victim also be a free Muslim to establish equivalence (mukafa'ah). A non-Muslim (Kafir) is not equivalent to a Muslim, nor is a slave equivalent to a free person.