The basic principle is that masturbation is haraam. Please see the answer to question no. 329
That is only permitted if a person fears that he may end up committing zina; no doubt the prohibition on zina is more emphatic, and it is more abhorrent and reprehensible. Hence it is permissible to commit the lesser of two evils so as to ward off the greater.
Ar-Ruhaybaani (may Allah have mercy on him) said: If a person, man or woman, masturbates with no need to do so, that action is haraam and he should be given a disciplinary punishment for it, because it is a sin. But if he does it because he fears falling into zina or homosexuality, or because he fears physical harm, then there is no punishment.
End quote from Mataalib Ooli an-Nuha Sharh Ghaayat al-Muntaha, 6/226
Al-Mirdaawi (may Allah have mercy on him) said:
We learn two things from this:
1. That masturbation is not permissible except in cases of necessity
2. The ruling for women on that matter is the same as the ruling for men, if a woman fears falling into zina.
This is the correct view, as stated in al-Furoo.
End quote from al-Insaaf, 10/252
What the husband must do is give his wife her rights to kind treatment. One of the most important matters to which he must pay attention in that regard is keeping her chaste so that she will not look at other men, and giving her her rights in matters of intimacy as much as possible, even if that means using aphrodisiacs and paying attention to nutrition.
If the husband reaches climax quickly, before his wife is satisfied, then he has to try hard to stimulate her first, even if that is with his hand or body, and not start to have intercourse until she is ready for that, and then she can reach climax through intercourse.
If the question is about masturbation with the hand, what difference is there between the husband's hand or her own hand? Why can't he do that for her, and why should she do that herself?
What we think is that the husband should do that, and it is better if it is before he has intercourse with her, then if she needs anything else, he can stimulate her again after having intercourse, so that her needs will be met.
There is nothing wrong with him consulting a specialist doctor, if he is suffering from any kind of problem.
And Allah knows best.
Reproduced from Islam QA