What is the ruling regarding a man saying to someone other than his wife, "This girl is forbidden to me through her offspring," while intending his wife?

A man's prohibition of his wife upon himself depends on his intention. If he intended divorce, it counts as such. If he intended ẓihār (a pre-Islamic form of divorce by likening one's wife to a forbidden female relative), it counts as such, and he must offer its expiation. If he intended it as an oath, or had no specific intention, it counts as an oath, and he must offer its expiation. This takes effect merely by uttering the words, whether the wife is present or absent.