What is the ruling on raising an infant "who is the child of zina" when his parents are unable to raise him? And is he considered a mahram to the family undertaking his care and upbringing when he reaches the age of responsibility, knowing that he did not suckle from the breast of anyone from those who undertook his care, and his parents do not acknowledge him and wish to get rid of him?

Raising an abandoned child (laqeet) and saving them from destitution is a communal obligation (fard kifaya), and there is a great reward in it. However, an abandoned child does not become a mahram (definition) to those who raise them merely by virtue of being raised. Rather, there must be a reason for mahramiyya such as fosterage (radha'ah), lineage, or marriage alliance (musahara). If no such reason exists, then the child is considered a non-mahram (ajnabi) and must be treated as such, especially after puberty. It is advisable for anyone wishing to raise an infant to have one of their women breastfeed the child so that they become a mahram. Nevertheless, it is not permissible to abandon the child to destitution simply because of the absence of mahramiyya.