﴿ وَإِذَا كُنتَ فِيهِمْ فَأَقَمْتَ لَهُمُ ٱلصَّلَوٰةَ فَلْتَقُمْ طَآئِفَةٌۭ مِّنْهُم مَّعَكَ وَلْيَأْخُذُوٓا۟ أَسْلِحَتَهُمْ فَإِذَا سَجَدُوا۟ فَلْيَكُونُوا۟ مِن وَرَآئِكُمْ وَلْتَأْتِ طَآئِفَةٌ أُخْرَىٰ لَمْ يُصَلُّوا۟ فَلْيُصَلُّوا۟ مَعَكَ وَلْيَأْخُذُوا۟ حِذْرَهُمْ وَأَسْلِحَتَهُمْ ۗ وَدَّ ٱلَّذِينَ كَفَرُوا۟ لَوْ تَغْفُلُونَ عَنْ أَسْلِحَتِكُمْ وَأَمْتِعَتِكُمْ فَيَمِيلُونَ عَلَيْكُم مَّيْلَةًۭ وَٰحِدَةًۭ ۚ وَلَا جُنَاحَ عَلَيْكُمْ إِن كَانَ بِكُمْ أَذًۭى مِّن مَّطَرٍ أَوْ كُنتُم مَّرْضَىٰٓ أَن تَضَعُوٓا۟ أَسْلِحَتَكُمْ ۖ وَخُذُوا۟ حِذْرَكُمْ ۗ إِنَّ ٱللَّهَ أَعَدَّ لِلْكَٰفِرِينَ عَذَابًۭا مُّهِينًۭا ﴾

“Thus, when thou art among the believers and about to lead them in prayer, let [only] part of them stand up with thee, retaining their arms. Then, after they have finished their prayer, let them provide you cover while another group, who have not yet prayed, shall come forward and pray with thee, being fully prepared against danger and retaining their arms: (for) those who are bent on denying the truth would love to see you oblivious of your arms and your equipment, so that they might fall upon you in a surprise attack. But it shall not be wrong for you to lay down your arms [while you pray] if you are troubled by rain or if you are ill; but [always] be fully prepared against danger. Verily, God has readied shameful suffering for all who deny the truth!”

When you O Muhammad (s) are present among them while you all fear an enemy and you stand to lead them in prayer this type of address is customary in the Qur’ān let a party of them stand with you while another party stand back and let them the party standing with you take their weapons with them. Then when they have performed their prostrations that is when they have prayed let them the other party be behind you on guard until you complete the prayers; thereupon let this party go on guard and let another party who have not prayed come and pray with you taking their precautions and their weapons with them until you have completed the prayers. The Prophet s did this once at Batn Nakhla as reported by the two Shaykhs Bukhārī and Muslim. The disbelievers wish when you have stood up to pray that you should be heedless of your weapons and your baggage that they may descend upon you all at once by making an assault against you and capturing you and herein is the reasoning behind keeping weapons on oneself. You are not at fault if rain bothers you or if you are sick to lay aside your weapons and not carry them this implies that when there is no such excuse it is compulsory to carry them and this is one of two opinions held by al-Shāfi‘ī on this matter; the other opinion is that this precaution constitutes a sunna and this is the more preferable opinion. But take your precautions against the enemy and be on your guard as best you can; God has prepared for the disbelievers a humiliating chastisement.