Does one's fast become void if one drank a little after the dawn prayer call, thinking that the call to prayer had not yet been made? And is he obligated to complete the fast or to break it? And must he restart the expiation fast from the beginning after having fasted forty days of it?

If a fasting person masturbates out of ignorance of the ruling, their fast is not invalidated. However, if they deliberately masturbate and semen is discharged, they are only required to make up the fast (qada'), without expiation (kaffara), according to the preferred view. Whoever is ignorant of the number of days they need to make up must continue fasting until they are certain their obligation has been fulfilled. If someone eats or drinks, thinking that dawn has not yet broken, and then it becomes clear that it had, their fast is valid, and no make-up is required. As for a wet dream (ihtilam) and the discharge of semen during sleep, it does not invalidate the fast.