What is the ruling on shaking hands with women?

Question : May Allah reward you. He asks: Is the saying of the Messenger (peace and blessings be upon him), "I do not shake hands with women," specific or general? We request a detailed explanation of this issue.

Answer : There is no harm in shaking hands with women who are mahram (relatives one may not marry). As for those who are not mahram, a man does not shake hands with a woman, even if she is advanced in age; he does not shake her hand. Even if she extends her hand to him, he should restrain his hand. This is a problem because some people have the custom that a brother’s wife shakes hands with her brother-in-law, meaning she shakes hands with her brother, and this is forbidden and not permissible. A paternal aunt’s daughter might shake hands with her cousin, or a wife’s mother might shake hands with her son-in-law. Yes, is there no harm? Is there no harm in a wife’s mother shaking hands with her son-in-law?
A wife’s sister shaking hands with her husband is not permissible. The rule, then, is that any woman who is not a mahram of a man, it is not permissible for him to shake her hand, whether he shakes it directly or through a barrier, and whether the woman is advanced in age or young. As for mahram women...