Is it permissible to use contraception without the husband's knowledge if the husband is violent and insists on having children, while the wife suffers from health issues and does not wish to become pregnant again?

The default principle is that both spouses have the right to procreate. Therefore, neither spouse is permitted to undertake any action that prevents conception without the other's permission. However, if there is a clear excuse for the woman, such as pregnancy causing her health harm, attested by doctors, then in this case the husband's right to permission is waived, based on the Prophet's (peace be upon him) saying: "There should be no harm nor reciprocating harm." The interest of preserving the woman's health takes precedence. The husband's poor treatment is not considered a justification for refraining from procreation.