Is a wife's Hajj valid if she performs it without her husband's knowledge and consent, despite his prior promise to her regarding Hajj and his failure to fulfill it?

A woman is not permitted to perform Hajj without her husband's consent. The husband must fulfill his promise to his wife regarding Hajj, especially if it was stipulated in the marriage contract, for the Prophet (peace be upon him) said: "The conditions most worthy of fulfillment are those by which you make intimacy lawful." If the promise was made after the contract, the correct view is that it is obligatory to fulfill it, unless it would cause harm to the husband.