Sayyidah Aishah (may Allah be pleased with her) says that the Messenger of Allah (peace and blessings be upon him) was asked about a man who finds wetness but does not remember having a wet dream. He (peace and blessings be upon him) said: "He should perform ghusl." And he was asked about a man who sees that he has had a wet dream but does not find any wetness. He (peace and blessings be upon him) said: "There is no ghusl upon him." Umm Sulaym (may Allah be pleased with her) said: If a woman sees that, is ghusl required of her? He (peace and blessings be upon him) said: "Yes, women are the counterparts of men."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 796