What is the ruling on masturbation by hand or with the help of his wife for a married man who is unable to have intercourse with his wife due to health reasons and fears falling into sin, given his inability to marry a second wife?

A Muslim is not permitted to practice masturbation. Whoever does so is considered an aggressor, as Allah Almighty says: (But whoever seeks beyond that, then those are the transgressors). It is permissible to enjoy one's wife in any position except during menstruation, post-natal bleeding (nifas), anal intercourse, and during the state of ihram. As for those who are unable to marry, they should fast, for the Prophet, peace and blessings be upon him, said: "O young people, whoever among you can afford to marry, let him do so, for it helps him lower his gaze and guard his chastity. And whoever cannot afford to marry, let him fast, for it will be a shield for him."