Sahih Bukhari Volume 1, Book 3, Hadith 130

حَدَّثَنَا مُحَمَّدُ بْنُ سَلاَمٍ، قَالَ أَخْبَرَنَا أَبُو مُعَاوِيَةَ، قَالَ حَدَّثَنَا هِشَامٌ، عَنْ أَبِيهِ، عَنْ زَيْنَبَ ابْنَةِ أُمِّ سَلَمَةَ، عَنْ أُمِّ سَلَمَةَ، قَالَتْ جَاءَتْ أُمُّ سُلَيْمٍ إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم فَقَالَتْ يَا رَسُولَ اللَّهِ إِنَّ اللَّهَ لاَ يَسْتَحْيِي مِنَ الْحَقِّ، فَهَلْ عَلَى الْمَرْأَةِ مِنْ غُسْلٍ إِذَا احْتَلَمَتْ قَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ إِذَا رَأَتِ الْمَاءَ ‏"‏‏.‏ فَغَطَّتْ أُمُّ سَلَمَةَ ـ تَعْنِي وَجْهَهَا ـ وَقَالَتْ يَا رَسُولَ اللَّهِ وَتَحْتَلِمُ الْمَرْأَةُ قَالَ ‏"‏ نَعَمْ تَرِبَتْ يَمِينُكِ فَبِمَ يُشْبِهُهَا وَلَدُهَا؟ ‏"

Narrated By Um Salama : Um-Sulaim came to Allah's Apostle and said, "Verily, Allah is not shy of (telling you) the truth. Is it necessary for a woman to take a bath after she has a wet dream (nocturnal sexual discharge?) The Prophet replied, "Yes, if she notices a discharge." Um Salama, then covered her face and asked, "O Allah's Apostle! Does a woman get a discharge?" He replied, "Yes, let your right hand be in dust (An Arabic expression you say to a person when you contradict his statement meaning "you will not achieve goodness"), and that is why the son resembles his mother."