Question: The Shaikh rahimahullah was asked about the one who had a wet dream in the daytime of Ramadan?
Answer: “Our answer regarding that is that his fast is valid, for verily a wet dream does not invalidate the fast because it [occurs] without his choice. The pen is lifted from him during sleeping. However, it is obligatory for a person to include in his day the remembrance of Allah, recitation of the Quran, the obedience of Allah, the Exalted, and not do like many people do in terms of staying up in the nights of Ramadan. Sometimes they stay up with an affair which does not benefit them, but harms them. And when it is the day, they spend the entire day in sleep. That is not necessary. Rather what is necessary is that a person make his fast a time for acts of obedience [to Allah], remembrance of Allah, recitation of Quran, and other than that from what draws near to Allah, the Exalted. And Allah Knows”.
[Majmoo’ al-Fatawa wal-Rasaail (19/284)]
Faisal Ibn Abdul Qaadir Ibn Hassan