Musnad Abu Ya'la al-Mawsili 115:351

Ubayd Allah narrated to us, Khalid and Yahya narrated to us, they said: Shu'bah narrated to us, from Qatadah, from Anas, from the Prophet (peace be upon him), who 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 desist from that, or their eyesight will surely be snatched away."