Is it permissible for a man to say to his wife's mother: "O my mother"?

The questioner:
May Allah reward you, Honorable Shaykh. This questioner says: It is our custom for a man to say to his wife's mother, "O my mother." Is this form of address permissible?

The Shaykh:
This is disliked. It is disliked because if it resembles

The questioner:
It is our custom for a man to say to his wife's mother, "O my mother." Is this permissible?

The Shaykh:
This is not disliked in a way that makes it forbidden; it is disliked as a matter of disapproval (makruh tanzihi). One should not say to his wife, "O my mother" or "O my sister," because this resembles zihar. One should also not say to her mother, "O my mother," because if she were his mother, it would mean that her daughter is forbidden to him. Therefore, this is disliked. Yes.