Sunan an-Nasa'i 870
It was narrated that Ibn Abbas said:
"There was a woman who used to pray behind the Messenger of Allah (ﷺ) who was beautiful, one of the most beautiful of people. Some of the people used to go to the front row to avoid seeing her, and some used to go to
the back row so that when they bowed they could see her from beneath their armpits. Then Allah revealed the words: 'To Us are
known those of you who hasten forward and those who lag behind."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا نُوحٌ، - يَعْنِي ابْنَ قَيْسٍ - عَنِ ابْنِ مَالِكٍ، - وَهُوَ عَمْرٌو - عَنْ أَبِي الْجَوْزَاءِ، عَنِ ابْنِ عَبَّاسٍ، قَالَ كَانَتِ امْرَأَةٌ تُصَلِّي خَلْفَ رَسُولِ اللَّهِ صلى الله عليه وسلم حَسْنَاءُ مِنْ أَحْسَنِ النَّاسِ - قَالَ - فَكَانَ بَعْضُ الْقَوْمِ يَتَقَدَّمُ فِي الصَّفِّ الأَوَّلِ لِئَلاَّ يَرَاهَا وَيَسْتَأْخِرُ بَعْضُهُمْ حَتَّى يَكُونَ فِي الصَّفِّ الْمُؤَخَّرِ فَإِذَا رَكَعَ نَظَرَ مِنْ تَحْتِ إِبْطِهِ فَأَنْزَلَ اللَّهُ عَزَّ وَجَلَّ ‏{‏ وَلَقَدْ عَلِمْنَا الْمُسْتَقْدِمِينَ مِنْكُمْ وَلَقَدْ عَلِمْنَا الْمُسْتَأْخِرِينَ ‏}‏ ‏.‏