Is it permissible for a man to shake hands with his wife’s mother and his wife’s sister?

The questioner : What is the ruling on a man shaking hands with his wife’s mother?

The Shaykh : His wife’s mother.

The questioner: Yes.

The Shaykh : Yes, it is permissible because she is a mahram (a relative one may not marry) to him. Likewise, it is permissible for him to shake hands with any mahram.

The questioner : What about his wife’s sister?

The Shaykh : It is not the same; she is not a mahram.

The questioner : What is the difference between the two?

The Shaykh : The difference is that she is not a mahram, because if he divorces his wife, her sister becomes permissible for him to marry.

The questioner: Yes.

The Shaykh : Perhaps you have understood.

The questioner : May Allah bless you.

The Shaykh : And may Allah bless you, if Allah wills.

The questioner : Peace be upon you, and Allah’s mercy and blessings.

The Shaykh : And upon you be peace, and the mercy of Allah and His blessings and His forgiveness.
The student : O Shaykh, is it permissible now? There is another person.

The Shaykh : That one has left. It is clear that if we were talking and the phone rang, we would hang up the first call and answer the second. But if we do not answer, it will start ringing, meaning it is gone. So, is there anything else? Because, as the brother just mentioned, some of the brothers have questions.