Book 3, Number 0614:

It is reported on the authority of 'A'isha that a woman came to the Messenger of Allah (may peace be upon him) and inquired: Should a woman wash herself when she sees a sexual dream and sees (the marks) of liquid? He (the Holy Prophet) said: Yes. 'A'isha said to her: May your hand be covered with dust and injured. She narrated: The Messenger of Allah (may peace be upon him) said: Leave her alone. In what way does the child resemble her but for the fact that when the genes contributed by woman prevail upon those of man, the child resembles the maternal family, and when the genes of man prevail upon those of woman the child resembles the paternal family.