His statement, “No slave suffices for any of the expiations except a believing slave”: someone may say that the apparent meaning of the author’s words is that every expiation involves the emancipation of a slave. But this is not so. Rather, he means those expiations in which a slave is to be emancipated; in them, only a believing slave suffices. They are: the expiation for zihar, the expiation for killing, the expiation for an oath, and the expiation for intercourse during Ramadan.
His statement, “except a believing slave”: this is an instance of using the part to refer to the whole. A part can only be used to refer to the whole when that part is indispensable to its existence. This is an important principle. That is, one cannot refer to a person as “a finger,” because a finger may be lost while life remains. As for the neck, if it is severed, the person dies. This is why, when Allah the Exalted refers to the prayer by its bowing and prostration, these are obligatory elements of it.
His statement, “believing”: this is the first condition. What is intended by faith here is the basic measure of faith, not complete faith; there is a difference between them. Complete faith is the perfect faith described in the saying of Allah the Exalted: “The believers are only those who, when Allah is mentioned, their hearts tremble; when His verses are recited to them, they increase them in faith; and upon their Lord they rely.” [al-Anfal: 2] As for the basic measure of faith, it includes one who has faith even if he does not possess these qualities; thus, it includes the sinful Muslim. What is intended, then, is the basic measure of faith, not complete faith.
Let us consider the evidence that faith is required in all the expiations. In the expiation for killing, faith is explicitly stipulated: “Whoever kills a believer by mistake must free a believing slave.” [al-Nisa’: 92] Regarding the expiation for an oath, Allah says: “Its expiation is to feed ten needy people with the average of what you feed your own families, or to clothe them, or to free a slave. But whoever cannot find the means must fast for three days.” [al-Ma’idah: 89]