Addressing one's wife with the words: "O my mother" and "O my sister"

The questioner:
He says: Honorable Shaykh, may Allah grant you success, if a man says to his wife, "O my mother" or "O my sister," and he does not intend to make her forbidden to him, but rather out of kindness toward her,

The Shaykh:
This is not permissible; it is disliked. It is disliked for a man to address his wife with the term of a mahram (a relative one may not marry), such as "O my sister" or "O my mother." This is not disliked because it resembles zihar (likening one's wife to a forbidden relative). Yes, one should avoid such wording. If he wants to honor her, he should honor her with other words. Yes, he should not say "O my sister," "O my mother," "O my aunt," or any other term for a mahram. Yes.

The questioner:
Is there a kaffarah (expiation) for this?

The Shaykh:
No, there is no kaffarah for this, but he should leave off this practice. Yes.