Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.091B.
Section : Raising one’s sight to the sky or upwards.
Abu Hurairah reports that the Messenger of Allah said: “Those who raise their sight to the sky during the prayer should stop doing so or their sight may be taken away.” This is related by Ahmad, Muslim, and an-Nasa’i.