كتاب الطهارة
1  
The Book of Purification
(6)
Chapter: The Nullification of Wudu
(6)
باب نواقض الوضوء
Bulugh al-Maram 82
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].
وَلِأَبِي دَاوُدَ أَيْضًا, عَنْ اِبْنِ عَبَّاسٍ مَرْفُوعًا: { إِنَّمَا اَلْوُضُوءُ عَلَى مَنْ نَامَ مُضْطَجِعًا } وَفِي إِسْنَادِهِ ضَعْفٌ أَيْضً ا 1‏ .‏


‏1 ‏- منكر.‏ رواه أبو داود (202)‏.‏

Reference : Bulugh al-Maram 82
In-book reference : Book 1, Hadith 99
English translation : Book 1, Hadith 88