Is ghusl required after a wet dream resulting from masturbation if one wakes up quickly and is unable to distinguish between semen and other secretions?

Masturbation is forbidden, and repentance from it is obligatory. Nocturnal emission (wet dream) is not considered masturbation. Whoever wakes up after a wet dream and finds wetness must perform ghusl (ritual bath), according to the more correct opinion, whether he knows the wetness is semen or is ignorant of its being semen.