Musnad Ahmad 32:486

Muhammad ibn Bishr narrated to us, Sa'id ibn Abi 'Aruba narrated to us, from Qatadah, from Anas ibn Malik, from the Prophet, peace and blessings of Allah be upon him, that he said: "What is the matter with people who raise their eyes toward the sky during their prayer?" He said: His speech regarding that became severe, until he said: "They must either cease from that, or their eyesight will surely be snatched away."