An-Nisa 4:102

Wa-itha kunta feehim faaqamta lahumuassalata faltaqum ta-ifatun minhummaAAaka walya/khuthoo aslihatahum fa-ithasajadoo falyakoonoo min wara-ikum walta/ti ta-ifatunokhra lam yusalloo falyusalloo maAAakawalya/khuthoo hithrahum waaslihatahumwadda allatheena kafaroo law taghfuloona AAan aslihatikumwaamtiAAatikum fayameeloona AAalaykum maylatan wahidatanwala junaha AAalaykum in kana bikum athanmin matarin aw kuntum marda an tadaAAoo aslihatakumwakhuthoo hithrakum inna AllahaaAAadda lilkafireena AAathaban muheena

And when you [i.e., the commander of an army] are among them and lead them in prayer, let a group of them stand [in prayer] with you and let them carry their arms. And when they have prostrated, let them be [in position] behind you and have the other group come forward which has not [yet] prayed and let them pray with you, taking precaution and carrying their arms. Those who disbelieve wish that you would neglect your weapons and your baggage so they could come down upon you in one [single] attack. But there is no blame upon you, if you are troubled by rain or are ill, for putting down your arms, but take precaution. Indeed, Allāh has prepared for the disbelievers a humiliating punishment.

When you (O prophet) are in their midst, and arrange for them the Salāh, then, a party from them should stand with you, and should take their arms along. Then, once they performed Sajdah, they should move away from you, and the other party, that has not yet performed Salāh, should come and perform Salāh with you, and should take their precautionary measures and their arms. Those who disbelieve would want you to become heedless to your arms and your belongings, so that they come down upon you in a single move. There is no sin on you, if you have some inconvenience due to rain, or you are sick, in putting your arms aside, but take your precautionary measures. Surely, Allah has prepared for the disbelievers a humiliating punishment.