(23, 24) “Forbidden to you for marriage are your mothers, your daughters, your sisters, your paternal aunts, your maternal aunts, your brothers’ daughters, your sisters’ daughters, your milk-mothers who nursed you, your milk-sisters, your wives’ mothers, your stepdaughters under your care—born of your wives with whom you have consummated marriage; but if you have not consummated marriage with them, there is no blame upon you—and the wives of your sons from your own loins. Also forbidden is marrying two sisters at the same time, except what has already occurred. Indeed, Allah is Ever-Forgiving, Most Merciful.”
These noble verses encompass the women prohibited by lineage, nursing, marital affinity, and simultaneous marriage, as well as those women who are lawful to marry. As for those prohibited by lineage, they are the seven categories mentioned by Allah.
The term “mother” includes every female ancestor through whom one’s line of descent passes, however remote. The term “daughter” includes every female descendant. Sisters include full sisters, paternal half-sisters, and maternal half-sisters. A paternal aunt is every sister of one’s father or of any paternal grandfather, however remote.
A maternal aunt is every sister of one’s mother or of any grandmother, however remote, whether that grandmother is entitled to inherit or not. Brothers’ daughters and sisters’ daughters include all their female descendants, however remote.
These are the women prohibited by lineage according to the consensus of the scholars, as the noble verse explicitly states. All women besides them fall under His words, “Lawful to you are all beyond these,” such as the daughters of one’s paternal aunt or paternal uncle and the daughters of one’s maternal uncle or maternal aunt.
As for those prohibited through nursing, Allah mentions the mother and the sister. His prohibition of the nursing mother—even though the milk is legally attributed not to her but to the man to whom it is ascribed—implicitly indicates that this man becomes a father to the nursling. Once fatherhood and motherhood are established, the relationships branching from them are likewise established, including their siblings, ascendants, and descendants (1).
The Prophet—peace and blessings be upon him—said, “Nursing prohibits what lineage prohibits.” The marriage prohibition therefore extends through the nursing woman and the man to whom the milk is attributed just as it extends through blood relatives, while on the nursling’s side it extends only to the nursling’s descendants. This is on condition that there be five separate nursings within the first two years of life, as explained by the Sunnah.
As for those prohibited through marital affinity, they are four categories: the wives of one’s male ascendants, however remote; the wives of one’s male descendants, however remote, whether those descendants are heirs or excluded from inheritance; and the mothers and grandmothers of one’s wife, however remote. These three categories become prohibited by the marriage contract alone.
The fourth is the stepdaughter—the daughter of one’s wife and all her female descendants. She does not become prohibited until the marriage with her mother has been consummated, as Allah says here: “Your stepdaughters under your care—born of your wives with whom you have consummated marriage”—to the end of the verse.
The majority of scholars have said that the words “under your care” are a qualification expressed by way of ⦗174⦘ what is ordinarily the case and carry no contrary implication. A stepdaughter is therefore prohibited even if she was never under the man’s care. Nevertheless, this qualification conveys two benefits:
First, it draws attention to the wisdom behind prohibiting marriage to a stepdaughter: she stands in the position of a daughter, so permitting marriage to her would be repugnant.
Second, it indicates that private seclusion with one’s stepdaughter is permissible, for she has the same status as one’s own daughters and similar female relatives under one’s care. Allah knows best.
As for women prohibited from being married simultaneously, Allah mentions and forbids marrying two sisters at the same time. The Prophet—peace and blessings be upon him—also prohibited marrying a woman together with her paternal or maternal aunt. Thus, whenever two women are related within a permanently prohibited degree—such that, were one assumed to be male and the other female, marriage between them would be prohibited—it is forbidden to be married to both simultaneously. This is because doing so gives rise to causes that sever ties of kinship.