We have not come across any specific text from the Fuqaha that either encourages or discourages breastfeeding nieces and nephews. However, it is mentioned that a woman should refrain from breastfeeding children unnecessarily, as this can complicate matters of Nikaah later in life.

It is advisable thus, to avoid unnecessarily breastfeeding nieces and nephews with the intention of making their cousins Mahram. The reason for this is that it could create complications if they later wish to marry one another. Moreover, the nature of the relationship between siblings and cousins is different. Brothers and sisters, due to sharing the same parents, household environment, and upbringing, are naturally less inclined to be attracted to one another, which reduces the risk of Fitnah when interacting as Mahrams.

Cousins, on the other hand, typically grow up in separate households, with different parents, environments, and habits, and are therefore more likely to be attracted to one another. If they are made Mahram through breastfeeding, it may result in free and casual interaction between them, and potentially be a cause of great Fitnah. For these reasons, we would not encourage unnecessarily breastfeeding nieces and nephews for the purpose of making them each other’s Mahram.