What is the ruling on one who supplicated against himself, asking for his hand to be severed if he practiced masturbation, then repeated the supplication with the phrasing, "If I do it more than 3 times a week," and then proceeded to do so? And what is the expiation required in these cases?

A Muslim is forbidden from invoking curses upon himself, his children, his servants, or his wealth, lest it coincide with an hour when Allah answers prayers. Therefore, it is wrong for a person to invoke curses upon himself to abstain from unlawful acts; rather, he should abandon them out of fear of Allah and supplicate to Allah to help him remain steadfast. Some scholars are of the opinion that invoking curses upon oneself in anger is idle talk for which there is no accountability, and they cite as evidence the Almighty's saying: ﴿And if Allah were to hasten for the people the evil [they invoke] as He hastens for them the good, their term would have been concluded for them.﴾ [Yunus: 11]. As for swearing an oath to abandon a sin, if it was an invocation of a curse upon oneself, then he must repent. But if it was an oath by Allah and he then broke it, he must offer expiation for breaking an oath.