Must the father of the sister's son give his consent for the child to be nursed so that he becomes a brother to the questioner's and her husband's children, or is the husband's consent sufficient?

A woman is permitted to breastfeed a child who is not her own, provided her husband grants permission, unless it becomes obligatory for her to breastfeed him, or there is a compelling need. The jurists have not stipulated the father's permission, especially if no harm accrues to the child as a result. The permissibility of breastfeeding is confirmed when there is a need for it, or when there is a recognized legitimate interest, such as breastfeeding the child so he becomes a brother to her children, thereby alleviating any discomfort regarding his mixing with her daughters, just as the Prophet, peace and blessings be upon him, permitted it for Salim, the freed slave of Abu Hudhayfah. It is preferable to seek the child's father's permission if possible.