Musnad Ahmad 32:206

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