Is the repentance of someone who practices masturbation and then repents, but repeatedly returns to it, accepted? Will he be held accountable for it? And what is the ruling on the prayers he previously missed?

One must repent from masturbation and renew repentance every time one returns to it, while adhering to the conditions of sincere repentance: abandoning the sin, regretting it, and resolving not to return to it. Sincere repentance is accepted and wipes away sins. Allah accepts repentance no matter how often the sin is repeated or how grave it is, and the door to repentance is not closed as long as the soul is in the body. This is stated in the Hadith (definition) Qudsi, after the servant's repeated repentance: "Do as you wish, for I have forgiven you." And in the Hadith: "If you did not sin, Allah would do away with you and bring people who would sin and then seek forgiveness, so He would forgive them." Steadfastness in repentance is aided by recalling the ugliness and danger of the sin, striving against the self, keeping company with the righteous, and making abundant supplication. As for the prayers missed before repentance, the majority view is that they must be made up, provided it does not harm the body or livelihood.