Sahih Muslim Book 24, Hadith Number 5236.

Chapter : It Is prohibited to lie down on one’s back and placing of one’s foot upon the other.

Jabir reported that Allah’s Messenger (may peace be upon him) forbade the wrapping of oneself completely leaving no room for the arm and supporting oneself when sitting with a single garment wrapped round one’s knees and a person raising one of his feet and placing it on the other while lying on his back.2512