Is istinjāʾ necessary after sleeping at night?

Sleep does not necessitate istinja’ (cleaning oneself after urinating or defecating) at all, and we are not aware of any differing opinion on this; because no text has been narrated to that effect in the Book of Allah or the Sunnah of His Messenger, and because istinja’ was prescribed to remove impurity, and there is no impurity in sleep or in passing wind.