Narrated Anas bin Malik: The Prophet (ﷺ) said, "What is wrong with those people who look towards the sky during the prayer?" His talk grew stern while delivering this speech and he said, "They should stop (looking towards the sky during the prayer); otherwise their eyesight would be taken away."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، قَالَ أَخْبَرَنَا يَحْيَى بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا ابْنُ أَبِي عَرُوبَةَ، قَالَ حَدَّثَنَا قَتَادَةُ، أَنَّ أَنَسَ بْنَ مَالِكٍ، حَدَّثَهُمْ قَالَ قَالَ النَّبِيُّ صلى الله عليه وسلم " مَا بَالُ أَقْوَامٍ يَرْفَعُونَ أَبْصَارَهُمْ إِلَى السَّمَاءِ فِي صَلاَتِهِمْ ". فَاشْتَدَّ قَوْلُهُ فِي ذَلِكَ حَتَّى قَالَ " لَيَنْتَهُنَّ عَنْ ذَلِكَ أَوْ لَتُخْطَفَنَّ أَبْصَارُهُمْ ".
sunnah.com