Sahih Bukhari
Prayers (Salat)
Volume: 001 / Book Number: 008 / Hadith Number: 464
Narrated 'Abbad bin Tamim:
that his uncle said, "I saw Allah's Apostle lying flat (on his back) in the mosque with one leg on the other." Narrated Said bin Al-Musaiyab that 'Umar and 'Uthman used to do the same.