What is the ruling on a husband hitting his wife after an argument over a trivial matter, and his saying to her: "Shut up or I'll hit you"?

If a wife disobeys her husband without a valid reason, Islam addresses this in stages: admonition and guidance, then abstaining from her bed. If these are ineffective, the husband is permitted to strike her a non-injurious blow, not including the face or humiliation, provided the intention is to discipline and reform her. He must cease striking her once she becomes obedient, in accordance with the Almighty's saying: "As for those [wives] from whom you fear defiance, admonish them, and abandon them in bed, and strike them. But if they obey you, do not seek a way against them. Indeed, Allah is ever Exalted, Grand."