Must the slave whose manumission is intended for expiation be a believer (Mu'minah)?

Primary text

According to the apparent position of the Madhhab, and the view of Malik, Shafi'i, and Abu Ubayd, the slave must be a believer. The evidence for requiring a believing slave is derived from the necessity of manumission involving facilitating the slave's worship of their Lord and completing their obligations and jihad, which aligns with the interests served by the expiation. This principle is inferred from the explicit requirement of a believing slave in the expiation for manslaughter (Quran 4:92), and this ruling is extended analogously to all manumission expiations.