Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.049A.
Section : Discharge of al-Mani owing to stimulation while asleep or awake.
The opinion of the jurists in general is that ghusl is a must should one have a discharge of al-mani (sperm) owing to stimulation while asleep or awake. Abu Sa’eed reported that he heard the Messenger of Allah, upon whom be peace, say, “Water (washing) is (needed) after (ejaculation of) sperm.” (Related by Muslim.)
Umm Salamah reported that Umm Sulaim said, “O Messenger of Allah, Allah is not ashamed of the truth. Does a woman have to perform ghusl if she has a wet dream?” He said, “Yes, if she sees the liquid.” (Related by al-Bukhari, Muslim and others.)
There are some other points of importance that need to be noted: