Sahih Muslim
The Book of Menstruation (Kitab Al-Haid)
Book Number: 003 / Hadith Number: 609
Anas b. Malik reported: A woman asked the Messenger of Allah (way peace be upon him) about a woman who sees in her dream what a man sees in his dream (sexual dream). He (the Holy Prophet) said: If she experiences what a man experiences, she should take a bath.