What is the ruling regarding someone who wakes from sleep and finds moisture?

If a sleeping person has a wet dream and semen is discharged, ghusl (ritual bath) becomes obligatory for him. However, if he has a wet dream but finds no semen, ghusl is not obligatory. If he wakes up and sees semen but does not recall a wet dream, he must perform ghusl. Similarly, if he wakes up and finds a discharge and does not know whether it is semen or something else, he must perform ghusl. Some jurists are of the opinion that ghusl is obligatory if there is a possibility that the discharge is semen. However, if the possibility is divided among three or more options (e.g., semen, madhy (pre-seminal fluid), phlegm), then ghusl is not obligatory, because the presence of semen in this case is weak.