What is the ruling regarding a man saying to his wife, "You are to me like the back of my mother," and what are the implications of that, knowing that he was unaware of the ruling on ẓihār? And do foreplay actions count as intercourse in this case?

Whoever says to his wife, "You are to me as the back of my mother" has committed ẓihār (a form of divorce), and this is a forbidden and reprehensible statement. He must offer the expiation mentioned in the Holy Quran, which is: freeing a slave before they touch each other. If he cannot find one, then fasting for two consecutive months before they touch each other. If he is unable to do that, then feeding sixty poor people.

If the intention behind the statement was to forbid intercourse for a specific period and that period elapsed without intercourse, then no expiation is required. However, repentance and seeking forgiveness are obligatory for any foreplay that occurred during that period, because it is not permissible to enjoy one's wife after ẓihār except after expiation. But if no specific period was intended, then the aforementioned expiation is obligatory.