Assalaamu alaykum, I would like to know who, if anyone, is responsible for keeping a record of a baby having been breastfed by a woman other than his mother in order to make this known when the baby grows up and wants to get married. I ask because I heard of a case where a couple had to separate after years of marriage because they discovered that as children they had been breastfed by the same wetnurse. They came from the same area of a country where sending children to a wetnurse is common. I cannot understand why they did not discuss this before concluding the marriage contract as that would have caused less distress. Is there any negligence on their part or on their parent's part for not having brought up this subject before finalising the marriage? May Allaah reward you.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger. 

Breastfeeding is important and it should be well kept; it is for this reason that the parents of the child should record every woman who breastfed their child out of fear that he would marry a woman among his female mahaarim (permanently unmarriageable) in the future, while ignoring it, and then he would discover after a long time that his wife is his sister through breastfeeding, as happens in some cases.

The commentary of Zaad al-Mustaqni’ authored by Sheikh Muhammad Muhammad al-Mukhtaar ash-Shinqeeti reads:

“This happens – we ask Allaah to protect us from it – in some incidents – that came across our hands – that a woman discovered – while she did not know about this before – that she spent 20 years (as wife) with her brother from breastfeeding – and they had children; this is evidence that one should be cautious about breastfeeding and that the mother and the parents of both children should fear Allaah and keep a record of the breastfeeding. If the mother has a son who was breastfed, then she must inform him and tell him: O son, you were breastfed by so and so, and identify the woman from whom he breastfed to him, and a sister also, if she knows that her brother was breastfed, then she should clarify this to him as well, so that he will not fall into what is forbidden, because these things are very harmful if people are lax about them. Some scholars stated that a man who had been informed that his wife was his sister (through breastfeeding) lost his mind as he was unable to bear the shock. This happens to women as well; this is evidence that the harm is very great, and people should therefore be cautious about this.” 

There are some scholars who said that the nursing mother herself should record the name of the child whom she breastfed, and she should inform the people that she had breastfed him until this matter becomes known and widespread among them.

Radd al-Muhtaar authored by Ibn ‘Aabideen from the Hanafi School reads, “The women are obliged not to breastfeed every child without necessity, and if they breastfed any children, then they should record that and spread it among the people and write it down as a precaution.”

Allaah knows best.