Evidence that sleeping while sitting does not invalidate wudu’
حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ الْعَنْبَرِيُّ، حَدَّثَنَا أَبِي، حَدَّثَنَا شُعْبَةُ، عَنْ عَبْدِ الْعَزِيزِ بْنِ صُهَيْبٍ، سَمِعَ أَنَسَ بْنَ مَالِكٍ، قَالَ أُقِيمَتِ الصَّلاَةُ وَالنَّبِيُّ صلى الله عليه وسلم يُنَاجِي رَجُلاً فَلَمْ يَزَلْ يُنَاجِيهِ حَتَّى نَامَ أَصْحَابُهُ ثُمَّ جَاءَ فَصَلَّى بِهِمْ .
Anas b. Malik reported: (The people) stood up for prayer and the Messenger of Allah (ﷺ) was talking in whispers with a man, and he did not discontinue the conversation till his Companions dozed off; he then came and led the prayer.