Q. I have a 5 month old baby and my sister in law has a 1 year old son. Could you all inform me about the laws concerning nursing each other’s babies and becoming foster siblings?
A. There is no harm if you nurse the son of your sister in law, and there is no harm if your sister in law nurses your baby. However, through this, you will become the foster mother of her child, and she will become the foster mother of your child. Both of these siblings will grow up to be connected to each other through fosterage, which will have the same law of real brothers/sisters.
Her son will also become a foster brother to all your children whom you have nursed, and your child will be a foster brother/sister to all the children whom she has nursed. This means that marriage will be permanently prohibited between these children.
And Allah knows best.
Mufti Waseem Khan