سُنَنُ النَّسَائِيِّ
Sunan an-Nasa’i 721
The Book of the Masjids
Lying On One's Back In The Masjid
أَخْبَرَنَا قُتَيْبَةُ، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ عَبَّادِ بْنِ تَمِيمٍ، عَنْ عَمِّهِ، أَنَّهُ رَأَى رَسُولَ اللَّهِ صلى الله عليه وسلم مُسْتَلْقِيًا فِي الْمَسْجِدِ وَاضِعًا إِحْدَى رِجْلَيْهِ عَلَى الأُخْرَى .
It was narrated from 'Abbad bin Tamim, from his paternal uncle, that he saw the messenger of Allah (ﷺ) lying on his back in the Masjid, placing one leg on top of the other.
Sunan an-Nasa'i, 721Sahih (Darussalam)