Ibn Majah

Commentary:
(1)
The string or rope with which a pouch containing gold coins, etc., is tied is called "wikā’." Unless the wikā’ is untied, nothing can come out of the pouch. In other words, it acts as a protector of the contents inside the pouch. Similarly, in the state of wakefulness, a person is aware whether his ablution (wudu) is intact or has been nullified due to the passing of wind. When the eyes are closed in sleep, control over the body is lost, as if the binding has been loosened, and one does not feel the passing of wind; therefore, sleep itself has been declared as something that nullifies ablution.

(2)
In general circumstances, sleep causes the ablution to be nullified; hence, the command for ablution after sleep has been given. Likewise, in some other rulings in the Shari‘ah, a thing that leads to a certain result is given the same ruling as that result itself, so that a person does not fall into doubts and uncertainties. For example: if drinking a large quantity of a beverage causes intoxication, then even a small quantity of it has been declared unlawful (haram). This is so that a person does not think that drinking one glass of a certain wine will not cause intoxication, and then, thinking this, drinks a glass and becomes intoxicated; therefore, even one glass is unlawful, even if it does not cause intoxication.

(3)
Shaykh al-Albani rahimahullah has graded this hadith as hasan.