Is it permissible for a Muslim to swear by Allah that he will never smoke again, and expose himself to the curse of Allah if he does not fulfill his oath (such as by saying: "The curse of Allah be upon me if I smoke again")? And if it is not permissible, then what should one who has done so out of ignorance do?

It is forbidden for a man to swear by cursing himself or by kufr (disbelief) or similar things, as these are blameworthy actions that could lead to his destruction. The Prophet, peace and blessings be upon him, also forbade cursing oneself, one's children, and one's wealth.

As for one who swears by such things, scholars have differed regarding the necessity of expiation (kaffarah) for him. Some have deemed it obligatory, while others, such as Ibn Qudamah and Sheikh Abdullah bin Jibreen, have not, holding that no expiation is required of him, and he only needs to repent. To avoid disagreement, a Muslim should offer the expiation for an oath.