(6) باب نواقض الوضوء
And Ibn 'Abbas (rad) narrated in a Marfu' (traceable) Hadith that:
"Ablution is necessary for one who sleeps while he is lying flat. [Reported by Abu Da'ud and there is weakness in its chain of narrators].
Reference: Bulugh al-Maram 82
In-book reference: Book 1, Hadith 99
English translation: Book 1, Hadith 88