Surah An-Nisa · 4:102

وَإِذَا كُنتَ فِيهِمْ فَأَقَمْتَ لَهُمُ الصَّلَاةَ فَلْتَقُمْ طَائِفَةٌ مِّنْهُم مَّعَكَ وَلْيَأْخُذُوا أَسْلِحَتَهُمْ فَإِذَا سَجَدُوا فَلْيَكُونُوا مِن وَرَائِكُمْ وَلْتَأْتِ طَائِفَةٌ أُخْرَىٰ لَمْ يُصَلُّوا فَلْيُصَلُّوا مَعَكَ وَلْيَأْخُذُوا حِذْرَهُمْ وَأَسْلِحَتَهُمْ ۗ وَدَّ الَّذِينَ كَفَرُوا لَوْ تَغْفُلُونَ عَنْ أَسْلِحَتِكُمْ وَأَمْتِعَتِكُمْ فَيَمِيلُونَ عَلَيْكُم مَّيْلَةً وَاحِدَةً ۚ وَلَا جُنَاحَ عَلَيْكُمْ إِن كَانَ بِكُمْ أَذًى مِّن مَّطَرٍ أَوْ كُنتُم مَّرْضَىٰ أَن تَضَعُوا أَسْلِحَتَكُمْ ۖ وَخُذُوا حِذْرَكُمْ ۗ إِنَّ اللَّهَ أَعَدَّ لِلْكَافِرِينَ عَذَابًا مُّهِينًا

“When you [O Prophet] are [campaigning] with them and you lead them in prayer, let one group of them pray with you — while armed. When they prostrate themselves, let the other group stand guard behind them. Then the group that has not yet prayed will join you in prayer — and let them be vigilant and armed. The disbelievers would wish to see you neglect your weapons and belongings, so they could launch a sweeping assault on you. But there is no blame if you lay aside your weapons when overcome by heavy rain or illness — but take precaution. Indeed, Allah has prepared a humiliating punishment for the disbelievers.”