What is the ruling on swearing by the phrase: "Divorce be upon me" or "By divorce upon me," and is this considered swearing by other than Allah, which leads to shirk (polytheism), and what is its expiation?

Scholars have differed regarding the ruling on swearing by divorce, oscillating between disliking it (makrooh) and prohibiting it (haraam). Swearing by divorce is not a true oath; rather, it is a conditional pronouncement of divorce and an obligation that takes effect upon the occurrence of the condition. Therefore, it does not fall under the purview of the Hadith: "Whoever swears by other than Allah has committed shirk." Its expiation is seeking forgiveness (istighfar) and repentance (tawbah).