What is the ruling on saying "You are unlawful to me if you do not stay away from Facebook" with the intention of frightening, and repeating it twice, knowing that the wife refused to abstain, then they reconciled and she returned to say "I can stay away from it, but I will remain unlawful to you," then the husband had intercourse with her, ignorant that this is ẓihār, and is this considered ẓihār, what is its expiation, how should the wife be treated, and what is the ruling for one who cannot fast?

The suspension of the prohibition of the wife from Facebook takes effect if she does not desist from it, and this can be immediate or delayed, depending on the intention or the surrounding circumstances. The default is that it is delayed.

If you intended only to scare your wife with this prohibition, then you are liable for an expiation for breaking an oath (kaffarat yamin) if the prohibition is violated. You are not liable for Zihar, and the expiation is not repeated by repeating the words of prohibition.

The expiation for an oath is to feed ten needy persons, or clothe them, or emancipate a slave. If you are unable to do these three, then you must fast for three days. You should not resort to fasting unless you are unable to perform the other three options. If you are unable to fast, the expiation remains a debt upon you until you are able to fulfill it. Your wife remains under your marital bond, and there is no punishment or expiation upon you regarding your marital relations with her.