We have enjoined man to be kind to his parents. His mother has carried him in travail, and bore him in travail, and his gestation and weaning take thirty months. [46: 15]
The mother's role clearly extended past birth to breastfeeding until the child was on to solid foods. Muslim philosophers went further: "No milk is more blessed than mother's milk for the infant." and "There is no better milk for an infant than mother's milk." are some of the statements found that expanded on the Koran's verse.
There is also:
And if you wish to have your children nursed by a substitute, there is no blame upon you as long as you give payment according to what is acceptable. [2:233]
Because of the practice of employing a wet nurse—a woman other than the baby's biological mother to breastfeed the baby—another discussion arose: if kinship is established by the action of breastfeeding, what does that mean for the future of the child?
In Western Europe, "milk siblings"—children linked by different mothers but by the same wet nurse—could be raised together, the wet nurse's child receiving some of the same benefits as the employer's child. Alexander Neckham, born on the same day as the future King Richard I of England, was raised alongside him in his early years, since Neckham's mother, Hodierna, was employed to live in the palace and nurse both babies. (It was believed that only a woman who had just given birth could lactate, so to find a wet nurse you would seek a woman who had just had her own child.)
In Islamic law, however, "milk kinship" (rida'a) presented an issue that was apparently not a concern in Europe. Because of the bond created between mother and child, children nursed by the same woman experience "milk kinship" which is a bond strong enough that marriage between them would be considered incestuous. Families must be known to each other to prevent inappropriate marriages.
This is an issue in modern times, because:
Prohibited to you [for marriage] are…your milk mothers who nursed you and your sisters through nursing…[Nisa 4:23]
There are HMBs (Human Milk Banks) for infants in hospitals. These are usually from donor mothers, and the milk is mixed. There is no way to know whence comes the milk fed to a baby that needs it. Therefore, when the baby is old enough to consider marriage, it is impossible to know whether he/she has any "milk kinship" with a potential mate.
Of course, the Koran comes from the sayings and experiences of Muhammad. What we have been talking about is no different. Muhammad had a wet nurse, and tomorrow we'll see a brief biography of Halima bint Abi Dhu'ayb.