ENOfficial
It was narrated from Anas bin Malik that: The Messenger of Allah (ﷺ) 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."
Source: sunnah.com
Other translations
Arabic
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 " .
sunnah.com