Sahih Muslim Book 004, Number 0862:

Jabir b. Samura reported: The Messenger of Allah (may peace be upon him) said: The people who lift their eyes towards the sky in Prayer should avoid it or they would lose their eyesight.

Sahih Muslim Book 004, Number 0863:

Abu Huraira reported: People should avoid lifting their eyes towards the sky while supplicating in prayer, otherwise their eyes would be snatched away.