It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that a beautiful woman used to pray behind the Prophet Muhammad (peace and blessings be upon him). Some people would stand in the front rows with the intention that they would not see her, and some people would stand in the last rows with the intention that when they bowed (in ruku‘), they could see her from under their armpits. So Allah Almighty revealed this command: {وَلَقَدْ عَلِمْنَا الْمُسْتَقْدِمِینَ مِنْکُمْ وَلَقَدْ عَلِمْنَا الْمُسْتَأْخِرِینَ} … We know those of you who go forward and We know those who lag behind.