It is narrated from Sayyida Aisha (may Allah be pleased with her), the Messenger of Allah (peace and blessings be upon him) said regarding the person who finds wetness upon waking but does not remember a dream (of ejaculation): "He should perform ghusl. And if he sees a wet dream but does not find any wetness, then ghusl is not obligatory upon him." (That is, ghusl becomes obligatory only when the effect of semen is seen, not merely by seeing a dream.)