Musannaf Ibn Abi Shayba 3:445

Abu Bakr narrated to us, he said: Yahya ibn Ghassan Abu 'Awanah narrated to us, from Mughirah, from al-Harith, who said: The sick person, if he is unable to sit, shall pray while lying on his back. He shall place his feet towards the direction of the Qibla, and he shall face the Qibla with his face, gesturing with his head.