Sayyidah Aishah (may Allah be pleased with her) says that a woman said: O Messenger of Allah, should a woman perform ghusl when she has a wet dream or sees the water? He (peace and blessings be upon him) said: "Yes." Aishah (may Allah be pleased with her) said to her: May your hands be covered with dust! The Messenger of Allah (peace and blessings be upon him) said: "Leave her. The resemblance comes only from this. When the woman's water prevails over the man's water, the child resembles his maternal uncles, and when the man's water prevails, the child resembles his paternal uncles."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 794