أَخْبَرَنَا يُوسُفُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا حَجَّاجٌ، عَنْ شُعْبَةَ، قَالَ سَمِعْتُ عَطَاءً الْخُرَاسَانِيَّ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، عَنْ خَوْلَةَ بِنْتِ حَكِيمٍ، قَالَتْ سَأَلْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم عَنِ الْمَرْأَةِ تَحْتَلِمُ فِي مَنَامِهَا فَقَالَ ‏"‏ إِذَا رَأَتِ الْمَاءَ فَلْتَغْتَسِلْ ‏"‏ ‏.‏

It was narrated that Khawlah bin Hakim said: "I asked the Messenger of Allah (PBUH) about a woman who has a wet dream and he said: 'If she sees water, let her perform Ghusl.'" Translation Not Available

Book Ref: Sunan An Nisai Book 1 Hadith 198
Web Ref:  Sunan An Nisai Not Available