What is the ruling on one person saying to another, "By 'haram' and 'talaq' that you saw," in response to the latter's statement, "By 'haram' and 'talaq' that I did not see such and such," knowing that the speaker did not intend divorce and the other person did not see it?

The majority of scholars hold that swearing by divorce results in divorce upon breaking the oath, contrary to Ibn Taymiyyah, who considers it to have the ruling of an oath by Allah, requiring an expiation for an oath. As for swearing by something forbidden (Al-Haraam), scholars have differed, and what is considered authoritative by us is that it depends on what the swearer intended. If he intended divorce, it is a divorce. If he intended ẓihār (a form of divorce), it is ẓihār. If he intended an oath or did not intend anything, an expiation for an oath becomes obligatory. If you swore based on your assumption, then do not break your oath. If you were doubting or intending to lie, then you have broken your oath. The legitimate oath is swearing by Allah the Almighty.