What is the ruling for one who masturbates with his hand unintentionally causing semen to be emitted? Does this invalidate his fast, and is he required to make up the fast and offer expiation?

It is not permissible to toy with the ذكر (penis) seeking lust. If semen is expelled by a deliberate act, it is masturbation, which invalidates the fast and necessitates making up the day. This is based on Ibn Qudamah's statement: "If he masturbates with his hand, he has committed something forbidden, and his fast is not invalidated by it unless he ejaculates. If he ejaculates, his fast is invalidated." However, if semen is not expelled, there is no breaking of the fast, based on Ibn Uthaymeen's statement: "If he masturbates without ejaculation, then he does not break his fast." Therefore, making up the day and sincere repentance are obligatory.