Is a wife's statement to her husband: "You are to me like my brother, to me like the back of my brother," considered a dhihār? And what is the expiation incumbent upon her?

It is forbidden for a Muslim to mock his brother, and for a husband to treat his wife well.

For a wife to say to her husband: "You are forbidden to me like my brother" is not ẓihār, but rather an expiable oath, because ẓihār can only be made by a man to his wife, and does not occur from a wife to her husband.

If a woman says to her husband: "You are to me like the back of my father or my brother," it is not ẓihār. Rather, its ruling is that of an oath, and it is not permissible for her to allow him access to her unless she performs an expiation for the oath.

The expiation for an oath is feeding ten poor people, or clothing them, or freeing a slave. If one cannot find any of these, then fasting for three days.