Musannaf Ibn Abi Shayba 1:882

Jarir ibn Abd al-Hamid narrated to us, from Abd al-Aziz ibn Rufay, from Ata, Abu Salamah ibn Abd al-Rahman, and Mujahid, who said: Umm Sulaym said, "O Messenger of Allah, a woman sees in her sleep what a man sees; is ghusl (ritual bathing) obligatory upon her?" He said, "Does she experience desire?" She said, "Perhaps." He said, "Does she experience wetness?" She said, "Perhaps." He said, "Then she must perform ghusl." Some women met her and said to her, "You have disgraced us before the Messenger of Allah, may Allah bless him and grant him peace." She said, "By Allah, I would not stop until I knew whether I was in a state of permissibility or prohibition."