حَدَّثَنَا إِبْرَاهِيمُ بْنُ مُوسَى الرَّازِيُّ، وَسَهْلُ بْنُ عُثْمَانَ، وَأَبُو كُرَيْبٍ - وَاللَّفْظُ لأَبِي كُرَيْبٍ - قَالَ سَهْلٌ حَدَّثَنَا وَقَالَ الآخَرَانِ، أَخْبَرَنَا ابْنُ أَبِي زَائِدَةَ، عَنْ أَبِيهِ، عَنْ مُصْعَبِ بْنِ شَيْبَةَ، عَنْ مُسَافِعِ بْنِ عَبْدِ اللَّهِ، عَنْ عُرْوَةَ بْنِ الزُّبَيْرِ، عَنْ عَائِشَةَ، أَنَّ امْرَأَةً، قَالَتْ لِرَسُولِ اللَّهِ صلى الله عليه وسلم هَلْ تَغْتَسِلُ الْمَرْأَةُ إِذَا احْتَلَمَتْ وَأَبْصَرَتِ الْمَاءَ فَقَالَ ‏"‏ نَعَمْ ‏"‏ ‏.‏ فَقَالَتْ لَهَا عَائِشَةُ تَرِبَتْ يَدَاكِ وَأُلَّتْ ‏.‏ قَالَتْ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ دَعِيهَا وَهَلْ يَكُونُ الشَّبَهُ إِلاَّ مِنْ قِبَلِ ذَلِكِ إِذَا عَلاَ مَاؤُهَا مَاءَ الرَّجُلِ أَشْبَهَ الْوَلَدُ أَخْوَالَهُ وَإِذَا عَلاَ مَاءُ الرَّجُلِ مَاءَهَا أَشْبَهَ أَعْمَامَهُ ‏"‏ ‏.‏

It is reported on the authority of 'A'isha that a woman came to the Messenger of Allah (PBUH) 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 (PBUH) 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. Translation Not Available

Book Ref: Sahih Muslim Book 3 Hadith 613
Web Ref:  Sahih Muslim Book 3 Hadith 314 b