Does a man's touching his private parts while fasting affect the validity of the fast?

A man's mere touching of his penis does not invalidate the fast, unless semen is discharged from it, in which case his fast becomes void. If touching the penis was for the purpose of masturbation, then he has disobeyed Allah Almighty, and he must repent and seek forgiveness. The preponderant opinion regarding the ruling on masturbation, when semen is discharged, is that expiation is not obligatory; rather, what is obligatory is making up the fast and seeking forgiveness.