Hazrat Ibn Abbas (may Allah be pleased with both of them) says that if one experiences a wet dream but does not see any wetness, then ghusl is not obligatory; but if one does not remember a wet dream but sees wetness, then ghusl is obligatory.

Hazrat Abu Hamza narrates that once I was traveling on my mount in a state between sleep and wakefulness when I felt arousal. I denied my self, but a little fluid was discharged from me, which moistened the root of my thigh, and nothing else happened. I asked Hazrat Ibn Abbas (may Allah be pleased with them both) about this, and he said: Wash your private part and the place where you feel wetness. He did not instruct me to perform ghusl (ritual bath).

Ibrahim says that if a person sees in a dream that he has had intercourse but does not feel any wetness upon waking, then ghusl is not obligatory.

It is also narrated similarly from Ibrahim.

It is also narrated similarly from Hazrat Sha'bi.

Hazrat Ibn Umar (may Allah be pleased with both of them) was asked about a person who, upon waking from sleep, finds wetness. He replied: If this happened to me, I would perform ghusl (ritual bath).

Ibrahim was asked about a person who sees wetness after waking up, so he said that he should perform ghusl (ritual bath).

Hazrat Mujahid says that ghusl is not obligatory until one is certain of having become junub.

Hazrat Saeed bin Jubair and Hazrat Ata say that when one sees semen, one should perform ghusl (ritual bath).

Hazrat Sha’bah says that I asked Hazrat Hakam and Hammad about the person who wakes up and sees wetness. So Hazrat Hakam said he should not perform ghusl. Hazrat Hammad said if he remembers having a wet dream, then he should perform ghusl.