What is the ruling on saying, "I divorce three times that she will not return," with the intention of stopping the mother from talking about the subject, and not with the intention of divorce?

If you intended by "she does not return" that she does not return at any time, then whenever she returns, she is divorced threefold according to the majority of scholars. And if you intended her not returning within a specific time, then if she returns within that time, the divorce occurs, but if she returns after it, it does not occur. As for the view of Sheikh al-Islam, if you intended to prevent your mother from speaking about the matter and did not intend to effect a divorce, then you are liable for an expiation for breaking an oath.