Sahih Muslim Book 003, Hadith Number 0607.
Chapter : Bathing is obligatory for a woman after experiencing orgasm in dream.
Anas b. Malik reported: Umm Sulaim who was the grandmother of Ishaq came to the Messenger of Allah (may peace be upon him) in the presence of 'Aisha and said to him: Messenger of Allah, in case or woman sees what a man sees in dream and she experiences in dream what a man experiences (i.e. experiences orgasm)? Upon this 'Aisha remarked: O Umm Sulaim, you brought humiliation to women; may your right hand be covered with dust. He (the Holy Prophet) said to 'Aisha: Let your hand be covered with dust, and (addressing Umm Sulaim) said: Well, O Umm Sulaim, she should take a bath if she sees that (i.e. she experiences orgasm in dream).