Musnad Ahmad 907:159

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Musayyib ibn Rafi', from Tamim ibn Tarafah, from Jabir ibn Samurah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "People must cease raising their eyes toward the sky during prayer, or else their sight will not return to them."