If someone loses their intellect, their wudu is nullified.
The word for intellect (‘aql) has the meaning of preventing. A person’s intellect prevents him from committing a reprehensible act.
It has been narrated that if someone commits a sin, part of his intellect departs and never returns. The meaning of this is that committing a sin dims the light of a person’s faith and intellect. If he repents and performs a good deed, it will wipe out the effect of the sin but it will not make up for the loss of intellect. Had he not committed the sin in the first place, the light of his faith and intellect would have increased.
The scholars also agree that sleeping nullifies your wudu, although they differ on the details.
Allah made sleep a manifestation of mankind’s weakness. No one can say that he can do without sleep, except those who have undertaken spiritual struggle (mujahadah) in the correct way. Someone on the spiritual path strives to reduce four things: sleep, food, speech and contact with people.
This is the advice of Imam al-Haddad:
وكن في طعام والمنام وخلطة ** ونطق على حدِّ اقتصارٍ وقلةِ
Regarding food, sleep, mixing with others and speech make do with the minimum
Since sleep is a manifestation of our weakness and deficiency, Allah decreed that there is no sleep in Paradise. When we are in a state of joy in this life, we are unable to sleep. That joy passes, but the joy of Paradise never passes, so no one in Paradise ever sleeps. The people of the Fire do not sleep either, but this is due to the punishment they are receiving. May Allah protect us from the Fire.
One of the unique attributes of the Prophet ﷺ was that his wudu was not nullified when he fell asleep, even if he fell asleep lying down. He said about this: “My eyes sleep but my heart does not sleep.”
The Sacred Law teaches us the etiquettes of going to sleep. It has been said that if someone observes the etiquettes of going to sleep, it is as if they are awake even when they are asleep. Likewise, if someone fails to observe the etiquettes of going to sleep, it is as if they are asleep even when they are awake. This is because the heart is asleep.
Extracts from Sayyidi Habib Umar bin Hafiz’s classes on the rulings and etiquettes of purification from Habib Abdullah bin Husayn Balfaqih’s “Kifayat al-Raghib” in Shafi fiqh.