What is the ruling on the fast of one who masturbated during the daytime in Ramadan, and did not ejaculate semen, but reached the peak of lust and pleasure, and how can he expiate for that with his ignorance of the number of days?

The practice of masturbation is forbidden in Sharia. If semen is not discharged, the fast is not invalidated. However, repentance and seeking forgiveness are obligatory. But if semen is discharged after a period, even if it was prevented, the fast of that day is invalidated and its making up for it becomes necessary. It is obligatory to ascertain the number of days invalidated in order to make them up. Ghusl (ritual bathing) is not required for the movement of semen without its discharge.