Surah An-Nisaa (4) — Ayah 102

102. And when you (O Prophet ﷺ) are among the believers and lead them in prayer (during battle), let a group of them stand with you (for prayer) [139], keeping their weapons with them. When they have prostrated, let them fall back, and let another group, who have not yet prayed, come forward and pray with you, keeping their guard and weapons. The disbelievers wish that you neglect your weapons and belongings so they can attack you in a single assault. But there is no blame upon you if you are troubled by rain or are ill and lay aside your weapons, but still, be cautious. Surely, Allah has prepared a humiliating punishment for the disbelievers.

[139] In this verse, the method of Salat al-Khawf (the prayer of fear) has been described. There are several possible forms of Salat al-Khawf, and six or seven such forms are mentioned in the hadiths. These forms are such that if a follower has performed one rak‘ah with the imam, then will he perform the second rak‘ah himself when he gets the opportunity or not? And if he does, then how will he perform it? And what will be the form for Maghrib prayer, which is not shortened and remains three rak‘ahs? And most likely, this method is only for that emergency situation when the battle is not raging fiercely, because in the case of a fierce battle, there is no opportunity for congregation at all. As in the Battle of the Trench, the Asr prayer of most Muslims, including the Messenger of Allah ﷺ, was missed, which you ﷺ and the Mujahideen performed as qada (make-up) after sunset. Then after that, the Maghrib prayer was performed.
[بخاری، کتاب مواقیت الصلٰوۃ۔ باب من صلی بالناس جماعۃً بعد ذھاب الوقت]
In reality, the method of Salat al-Khawf depends to a great extent on the war conditions. If there is no opportunity for congregation, a person can pray alone, can pray on a mount, and can even pray by gestures. Only two things must be kept in mind: first, which method is better in the current war situation, then that should be adopted; and second, that in such conditions, one should not forget the remembrance of Allah. Now, in this regard, consider the following hadiths:
1. Sayyiduna Ibn Abbas ؓ says: "Allah has made obligatory through the tongue of your Prophet: four rak‘ahs in residence, two in travel, and one rak‘ah in fear."
[مسلم، کتاب الصلوۃ، باب صلٰوۃ المسافرین وقصرھا]
2.
Different Forms of Salat al-Khawf:

Sayyiduna Abu Hurairah ؓ says that the Prophet ﷺ camped between Dajnān and ‘Usfan. The polytheists said: "These Muslims have a prayer which is more beloved to them than their fathers and sons, and that is the Asr prayer. Therefore, gather your equipment and attack them all at once at that time." Meanwhile, Jibril ؑ descended and ordered the Prophet ﷺ to divide his companions ؓ into two groups. One group should pray with him, and the other group should stand behind them facing the enemy, wearing their shields and weapons. Then the second group should come and pray with you, and the first group should wear their shields and weapons. In this way, each group will perform one rak‘ah, and the Prophet ﷺ will perform two rak‘ahs.
[ترمذي، ابواب التفسير]
3. When someone asked Sayyiduna Abdullah bin Umar ؓ how to perform Salat al-Khawf, he would say: The imam should step forward, and some people should pray with him. The imam should lead them in one rak‘ah. The rest should stand between them and the enemy, not praying. When these people have performed one rak‘ah with the imam, they should move back, and those who have not prayed should come and perform one rak‘ah with the imam. The imam will have completed his (two rak‘ahs) prayer. Now both groups should complete one rak‘ah each in turn, so they will also have two rak‘ahs each. And if the fear is greater than this, then pray standing on your feet, walking, or on a mount, whether facing the qiblah or not. Imam Malik (may Allah have mercy on him) says that Nafi‘ said that Abdullah bin Umar ؓ narrated this from the Messenger of Allah ﷺ.
[بخاري، كتاب التفسير]
[140] In the mentioned verse, permission to remove weapons is given only in two cases. The first is when it is raining and clothes and weapons are getting wet. The second is when a person, due to illness, cannot bear to remain armed. Apart from these cases, there is no permission to remove weapons. Therefore, at the end, this command was emphatically repeated again and again. The words ﴿خُذُوْا حِذْرَكُمْ﴾ are used in a very broad sense; it means to remain alert and vigilant, to remain armed, and to adopt all means of protection. For example, guarding the trenches and taking refuge in them, keeping war equipment ready before the battle, being aware of the enemy's movements, thinking of countermeasures, being prepared for the enemy's attack even for a surprise attack—all this is included in the meaning of ﴿خُذُوْا حِذْرَكُمْ﴾. In the Prophetic era, weapons of war were the individual property of every fighter, but today, providing weapons of war is the responsibility of governments. Therefore, the factories manufacturing weapons, the stockpiles of weapons, and their protection from the enemy are also included in ﴿خُذٌوْا حِذْرَكُمْ﴾. In short, the protection of the nation and country, the measures for the protection of the army personnel, the protection of war equipment, keeping battle plans secret—all are included in this command. Today, the enemy first destroys the secure stockpiles of weapons or the arms factories through sudden attacks. Muslims have been alerted to all these matters in this verse.