Answer
Wa `alaykum as-salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fawa:
- It is permissible for a non-Muslim woman to breastfeed a Muslim child, because the basic principle in this regard is permissibility, and there is no evidence to the contrary. Likewise, a Muslim woman is allowed to breastfeed a non-Muslim child.
- The Islamic ruling does not change because of such breastfeeding. Whoever was a Muslim before breastfeeding remains a Muslim afterwards and whoever was a non-Muslim before breastfeeding likewise remains a non-Muslim.
In his response to your question, Sheikh `Atiyyah Saqr, former head of Al-Azhar Fatwa Committee, states,
Before puberty, a child whose parents have different religions follows of the nobler religion. If, for example, his father is Muslim while his mother is Jewish or Christian, he is considered Muslim. If his father is Magian while his mother is Jewish or Christian, he is Jewish or Christian according to the religion of his mother whose religion, in such case, is nobler than his father’s.
Upon puberty, one becomes legally competent and is regarded a Muslim, a Christian, a Jew, or whatever, according to what he/she was before puberty. If he/she abandons the religion of Islam, he/she is then an apostate. All these judgments pertain to blood-based paternity or maternity.
While paternity or maternity based breastfeeding have certain rulings in terms of marriage and its related issues but they do not extend to the breast-fed child’s religion.
Thus, it is permissible for a Muslim child to be breast-fed by a non-Muslim woman- particularly if there is no one else to do so- because there is no evidence of prohibition. If that child is breast-fed by her, he is still a Muslim; likewise, if a Muslim woman breast-feeds a Jewish or a Christian child, this child remains Jewish or Christian.
Therefore, a Muslim man who was breast-fed by a Christian or a Jewish woman is prohibited to marry her because she his foster mother. He is allowed to touch her, sit with her alone, and look at her while she is without a veil, and so on, just as with his real mother in suchlike matters. As for his religion, it is not affected by this breastfeeding.
For more, see thee fatwas:
Does Breastfeeding 8-year-old Nephews Make Them Mahram?
Should You Stop Breastfeeding to Fast Ramadan?
Is It Haram to Breastfeed after 2 Years in Islam?
Can I Breastfeed My Baby for 30 Months?
Allah Almighty knows best.