Musannaf Ibn Abi Shayba 3:3941

Ghundar narrated to us, from Shu'bah, from 'Ammar al-'Absi, who said: I heard Ibn Bashar saying: Hudhayfah said: "Does one of you not fear, when he raises his sight to the sky, that his sight will not return to him?"—meaning while he is in prayer.