A young man masturbated during the day in Ramadhaan while he was fasting, what is it that is binding upon him to do?
Masturbating during the day in Ramadhan invalidates (his) fast if he did it intentionally and expelled the sperm (i.e. ejaculated). If the fast was an obligatory one he must make that day up and repent to Allah Subhaanahu wa Ta'aala because masturbation is not permitted whether one is fasting or not. (This act of masturbation) is what the people call the secret habit.
- Fiqh and Fataawa