Sunan an-Nasa'i, Hadith 1193 ⓘ
It was narrated from Anas bin Malik that: The Messenger of Allah said: "What is the matter with people who lift their gaze to the sky when praying?" And he spoke sternly concerning that until he said: "They must stop that or they will certainly lose their eyesight."
أَخْبَرَنَا عُبَيْدُ اللَّهِ بْنُ سَعِيدٍ، وَشُعَيْبُ بْنُ يُوسُفَ، عَنْ يَحْيَى، - وَهُوَ ابْنُ سَعِيدٍ الْقَطَّانُ - عَنِ ابْنِ أَبِي عَرُوبَةَ، عَنْ قَتَادَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " مَا بَالُ أَقْوَامٍ يَرْفَعُونَ أَبْصَارَهُمْ إِلَى السَّمَاءِ فِي صَلاَتِهِمْ " . فَاشْتَدَّ قَوْلُهُ فِي ذَلِكَ حَتَّى قَالَ " لَيَنْتَهُنَّ عَنْ ذَلِكَ أَوْ لَتُخْطَفَنَّ أَبْصَارُهُمْ " .
also referenced under: Book 13, Hadith 15 (In-Book) & Volume 2, Book 13, Hadith 1194 (DarusSalam)