Does a man's saying to his wife, "You are forbidden to me as my sister and mother are forbidden to me," constitute ẓihār if she tells so-and-so about a certain matter, and then she does tell so-and-so about it, but the intended relationship is not ruined?

The husband's statement to his wife: "You are as forbidden to me as my sister and my mother" is an explicit pronouncement of Dhihar. The Dhihar here occurred upon the fulfillment of the conditional clause, which is the wife informing the woman of a certain matter, and not by disrupting the relationship between the woman and her fiancé. According to the majority of scholars, Dhihar has occurred, and the husband must abstain from conjugal relations with his wife until he pays the expiation for Dhihar mentioned in the Holy Quran.