Is the marriage contract considered null and void if the husband returns to smoking after the wife's family stipulated that he quit, knowing that he had taken the wife's consent for that?

The marriage is not nullified by the husband's return to smoking if it was stipulated that he quit. However, some scholars, such as the Hanbalis, allow the wife to demand annulment of the marriage (فسخ النكاح). They cite the Prophet's (peace be upon him) saying: "The conditions most worthy of fulfillment are those by which you make intimate relations lawful." In the fatwas of Sheikh Muhammad ibn Ibrahim, a woman is given the option to annul her marriage or remain in it if her husband had agreed to quit smoking and then returned to it. Nevertheless, the wife is advised not to rush into seeking annulment and to try to reform her husband. As for the view of the majority of scholars, the wife is not entitled to enforce this condition, and therefore she cannot request the annulment of the marriage.