It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her) that she asked the Prophet (peace and blessings be upon him) about a woman who experiences a wet dream. He (peace and blessings be upon him) said: "Does she feel desire?" She replied: Yes. He (peace and blessings be upon him) said: "Then let her perform the ritual bath (ghusl)."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19836