What is the ruling on complete (satiating) breastfeeds, and are they impermissible? What is the ruling on a single, non-satiating suckle? And what is the ruling on a wife breastfeeding a Christian child concerning the hijab and similar matters?

Scholars have differed regarding the quantity of breastfeeding that establishes prohibition, and the most authoritative opinion is that it is five full breastfeeds.

There is no sin in your wife's action of breastfeeding the child; rather, she will be rewarded for it, based on the Prophet's (peace be upon him) saying: "In every wet liver there is a reward."

If her breastfeeding of him reaches five breastfeeds, then he becomes a mahram to her and to her daughters with respect to looking at them. There is no difference in this regard between a Muslim and a non-Muslim, due to the generality of the evidence. This is supported by the fact that Abu Sufyan entered upon his daughter Umm Habibah before his conversion to Islam without a hijab.

As for other matters besides looking, such as seclusion and travel, the most authoritative opinion is that a non-Muslim is not like a Muslim. Thus, a Muslim woman should not travel with her unbelieving father because he is not a mahram to her by explicit text, even if he is a mahram to her in terms of looking.