Is it permissible to free a slave who is not a Muslim (non-believer) for the expiation of Zihar?
General Chapter
Al-Mughni
Book of Zihar
Primary text
It is required that the slave freed for expiation must be a believer. This is evidenced by the narration of Mu'awiyah ibn al-Hakam, where the Prophet (PBUH) asked the female slave, "Where is Allah?" and upon her answering, "In the heaven," and confirming his prophethood, he commanded, "Free her; for she is a believer." This explicitly conditions the permissibility of freeing her on her being a believer. Furthermore, since expiation through freeing is a form of purification, only a believing slave suffices, similar to the expiation for killing. The general ruling (unrestricted term) must be restricted by the specific ruling when the underlying rationale (causal factor) is present. Since it is agreed that the slave must be sound from obvious defects that impede labor, restricting it to being free from disbelief is more fitting.
Supporting text
The causal factor for the restriction is that the purpose is to transfer ownership of the slave's benefits, which is not fully achieved if the slave has a major defect impeding labor. This necessity of soundness from defects necessitates the restriction to faith, as disbelief is a greater defect than physical imperfections that do not severely hinder labor.