Sahih Muslim 376
Sahih Muslim · Book 3: The Book of Menstruation · Evidence that sleeping while sitting does not invalidate wudu’
Anas reported:
حَدَّثَنِي أَحْمَدُ بْنُ سَعِيدِ بْنِ صَخْرٍ الدَّارِمِيُّ ، حَدَّثَنَا حَبَّانُ ، حَدَّثَنَا حَمَّادٌ ، عَنْ ثَابِتٍ ، عَنْ أَنَسٍ ، أَنَّهُ قَالَ أُقِيمَتْ صَلاَةُ الْعِشَاءِ فَقَالَ رَجُلٌ لِي حَاجَةٌ . فَقَامَ النَّبِيُّ صلى الله عليه وسلم يُنَاجِيهِ حَتَّى نَامَ الْقَوْمُ - أَوْ بَعْضُ الْقَوْمِ - ثُمَّ صَلَّوْا .
(The people) stood up for the night prayer when a man spoke forth: I need to say something. The Apostle of Allah (ﷺ) entered into secret conversation with him, till the people dozed off or some of the people (dozed off), and then they said the prayer.