Is it permissible for a woman to shake hands with her sister’s husband or her husband’s brother?

Question:
Is it permissible for a woman to shake hands with her sister’s husband, or her husband’s brother? May Allah reward you with good.

Answer:
It is not permissible for a woman to shake hands with a non-mahram, meaning someone who is not among her mahram relatives; because this causes fitnah (trial, discord or temptation), and because the Prophet (peace and blessings be upon him) did not shake hands with women, and his hand never touched the hand of a woman who was not lawful for him. Rather, he would take the pledge of allegiance from women by words, and they would not pledge by handshakes as men do. And Allah the Exalted said: “Indeed, in the Messenger of Allah is an excellent example for you.” Also, as we mentioned, a woman shaking hands with a man who is not among her mahram relatives is fitnah (trial, discord or temptation) for her and fitnah for him. Yes. It is obligatory for Muslims to abandon customs that contradict the rulings of the Shari'ah (Islamic sacred law).
We know that there are customs among some people, or some tribes, or some lands where ignorance is widespread, but these customs must be referred back to the Shari'ah (Islamic sacred law). Whatever the Shari'ah (Islamic sacred law) approves of, there is no harm in it, and whatever contradicts the Shari'ah (Islamic sacred law) must be abandoned. Among these is women shaking hands with men who are not their mahram relatives, for this contradicts the Shari'ah (Islamic sacred law), and it must be abandoned, warned against, and prevented. Yes. May Allah reward you with good, and may Allah reward you.