Is it permissible for a sister to cut off relations with her adopted brother, who was not nursed by her mother, due to the absence of a blood relationship between them, and because he apostatized from Islam, and slandered and backbit about her? And should she greet him after his apostasy?

It is not permissible for this child to mix with this family or to look at their unmarriageable kin (mahram), nor is it permissible for her to shake his hand, be alone with him, or uncover herself in front of him, because he is not a mahram. She should not greet him with salam or return his salam as long as he is an apostate.