It was narrated from Khawlah bint Hakim that:She asked the Messenger of Allah about a woman who sees in her dream that which a man sees. He said: "She does not have to take a bath unless she has an orgasm, just as man does not have to take a bath unless he has an orgasm."
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَعَلِيُّ بْنُ مُحَمَّدٍ، قَالاَ حَدَّثَنَا وَكِيعٌ، عَنْ سُفْيَانَ، عَنْ عَلِيِّ بْنِ زَيْدٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، عَنْ خَوْلَةَ بِنْتِ حَكِيمٍ، أَنَّهَا سَأَلَتْ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ عَنِ الْمَرْأَةِ تَرَى فِي مَنَامِهَا مَا يَرَى الرَّجُلُ فَقَالَ " لَيْسَ عَلَيْهَا غُسْلٌ حَتَّى تُنْزِلَ كَمَا أَنَّهُ لَيْسَ عَلَى الرَّجُلِ غُسْلٌ حَتَّى يُنْزِلَ " .
IbnMaja
The Book of Purification and its Sunnah • Hadith 602