Sunan an-Nasa'i, Volume 1, Book 8, Hadith 722 (DarusSalam) ⓘ
It was narrated from 'Abbad bin Tamim, from his paternal uncle, that he saw the messenger of Allah lying on his back in the Masjid, placing one leg on top of the other.
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 .
also referenced under: Hadith 721 (Reference) & Book 8, Hadith 34 (In-Book)