Read and reflect on verse 594 from Surah An-Nisaa: AND WHEN you go forth [to war] on earth, you will incur no sin by shortening your prayers if you have reason to fear that those who are bent on denyin...
وَإِذَا ضَرَبْتُمْ فِي الْأَرْضِ فَلَيْسَ عَلَيْكُمْ جُنَاحٌ أَنْ تَقْصُرُوا مِنَ الصَّلَاةِ إِنْ خِفْتُمْ أَنْ يَفْتِنَكُمُ الَّذِينَ كَفَرُوا ۚ إِنَّ الْكَافِرِينَ كَانُوا لَكُمْ عَدُوًّا مُبِينًا
AND WHEN you go forth [to war] on earth, you will incur no sin by shortening your prayers if you have reason to fear that those who are bent on denying the truth might suddenly fall upon you: for, verily, those who deny the truth are your open foes.