At islamweb.net there was something that addressed these topics, headlined with attention-grabbing "His wife and son have regular incestuous relations together."
It appears to be an advice column. From the question...
Respected Sheikh, I am a man in my late sixties and recently discovered that my 33 year old wife has regular incestuous relations with my 17 years old son.A few things to note right away: 1. Although this is not written so as to make clear she is not the biological mother of his son, I think if she was the biological mother of the son that would have been explicitly stated, which is not. 2. She is closer in age to his son than she is him. 3. Seventeen year-old males generally are bursting with hormones and constantly wanting sex. Leave one alone all day with an attractive person and... well, this isn't surprising. 4. It is entirely possible that where they live 17-year-olds can legally consent to sex with 33-year-olds.
When I confronted them they denied it, but one day I came home unexpectedly and found them in the act. They repented and promised not to do it again.So this was a matter of cheating.
I am devastated and don’t know what to do. I beg you to tell me in the light of the Quran and hadith what course of actions I shall take.This is, of course, from a Muslim website. Being cheated on, especially when the other person is another person you thought you could trust, is painful. My advice would be to seriously consider if this is unacceptable, and if he needs her to only have sex with him, if he's going to be able to treat her right going forward without going batty. If not, then the marriage should be over. But he didn't ask me. Let's get to the response was given...
First, there was a statement of what sins were committed according to Islamic teaching.
However, if they had both truly repented, then they did well.I doubt they were unaware what the religious authorities would say. They were horny, and perhaps also in love. But we get some more Quranic verses anyway. Then...
Now, if your wife becomes righteous and shows good conduct, then you should keep her and have good marital relations with her and do not hold her accountable for what she had done, but you are obligated not to have sexual relations with her until you make sure that she is not pregnant from Zina by the passing of one menstrual period.
Also, you should be keen on disciplining both of your wife and son and teaching them the matters of their religion as what they did is mostly due to ignorance and negligence.
On the other hand, if you are suspicious about your son in the future, then you should take the matter firmly in hand and prevent him from being in seclusion with your wife and prevent her from appearing in his presence without Hijaab. Likewise, if you are suspicious about your wife, then there is no good in keeping her as your wife; rather you should divorce her so that she would not contaminate your bed and give birth to children who are not from you.Ah yes, this was all because she wasn't covered up in a Hijaab. Uh huh.
Finally, it should be noted that committing Zina is generally due to being lenient in matters that lead to it, like a woman appearing in front of men (other than her husband) in an inappropriate manner, like wearing revealing clothes and so forth. So, one should be careful about this.
I do find other cultures' perspectives interesting.
Something people need to keep in mind is that while the Westermarck Effect (reduced sexual attraction) is common between people raised together or by one another, it isn't there when you bring someone new into your adult/post-pubescent child's life, whether that is your new lover, partner or spouse, or any post-pubescent children they have. This man was attracted to this woman. Why wouldn't his son be, too? That doesn't excuse cheating; someone who needs monogamy and has received a pledge of monogamy should expect monogamy as long as they are not neglecting their partner. But if he was living under the assumption that his son and wife were unlikely to be attracted to each other on some level, it was a mistaken assumption, as demonstrated.