In general, my understanding is that you are not supposed to refuse your wife intimacy. However, it is also expressly forbidden to engage in intimacy while she is in a niddah state. Does the latter prohibition override the former? If so, why?
This is purely a hypothetical question, and I realize that in a case like this there might be larger issues at play that warrant consulting a rabbi. I'm just curious about how the conflict between these two obligations would be resolved.
Pesachim 72b discusses a woman who desires intimacy from her husband, and it is approaching the expected time of her period.
והאמר רבא חייב אדם לשמח אשתו בדבר מצוה סמוך לווסתה
The Gemara asks further: Even so, didn’t Rava say that a man is obligated to please his wife through a mitzva? That is to say, he must engage in sexual intercourse with her when she so desires, even if it is not the time of her conjugal rights. The Gemara answers that we are dealing with a case where it was near her expected date of menstruation, when sexual relations are prohibited due to a concern that the woman may already be menstruating or that she may begin to menstruate during the sexual act.
Rashi and Tosafos there explain that in Shevuos 18b it is derived that one must separate from their wife as she approaches the expected time of her period.
I would infer if one must separate from their wife just before they become a Niddah, even if she desires intimacy, all the more so when she is actually a Niddah.
It's obvious to me that the obligation to one's wife doesn't include times where she is prohibited. I'm not sure if I need a source for that. It's not like this prohibition (which incurs kares) overrides that prohibition (really, obligation). It's that there is no obligation, just like when she's not interested there's no obligation.
A stronger proof might be from Kesubos 72a, which lists, among infractions of דת משה (Torah law) that are grounds for divorce and forfeiture of the kesubah, משמשתו נדה, she engages in relations with him while niddah. The Gemara there (further down on the same page) gives two scenarios:
She claims to have brought a discharge to Rabbi X and that he declared it not niddah blood (and on that basis, the husband engages in relations with her). Later on he checks with Rabbi X, who tells him that this is untrue.
Her neighbors know that she's niddah (because she's wearing the kind of clothes that she typically does at that time), but tells her husband that she's tahor, and on that basis they engage in relations.
(Tosafos there adds another possibility: he sees blood on her clothes, but she claims that it came from some other source.)
Clearly in all of these cases she wants to be intimate, but that doesn't make it permissible for either of them.
All of this is cited as halachah in Shulchan Aruch, Even Haezer 115:1-2.
