Muwatta Malik, Book 9, Hadith 90 (USC-MSA)

Yahya related to me from Malik from Ibn Shihab from Abbad ibn Tamim from his paternal uncle that he saw the Messenger of Allah, may Allah bless him and grant him peace, lying down in the mosque with one foot on top of the other.

وَحَدَّثَنِي 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 ‏.‏

sunnah.com

also referenced under: Book 9, Hadith 421 (In-Book)

Yahya related to me from Malik from Ibn Shihab from Said ihn al-Musayyab that Umar ibn al Khattab and Uthman ibn Affan, may Allah be pleased with them, used to do the same.

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، أَنَّ عُمَرَ بْنَ الْخَطَّابِ، وَعُثْمَانَ بْنَ عَفَّانَ، - رضى الله عنهما - كَانَا يَفْعَلاَنِ ذَلِكَ ‏.‏

sunnah.com

also referenced under: Book 9, Hadith 422 (In-Book)