وَإِذَا ضَرَبْتُمْ فِى ٱلْأَرْضِ فَلَيْسَ عَلَيْكُمْ جُنَاحٌ أَن تَقْصُرُوا۟ مِنَ ٱلصَّلَوٰةِ إِنْ خِفْتُمْ أَن يَفْتِنَكُمُ ٱلَّذِينَ كَفَرُوٓا۟ ۚ إِنَّ ٱلْكَٰفِرِينَ كَانُوا۟ لَكُمْ عَدُوًّۭا مُّبِينًۭا
And when you travel throughout the land, there is no blame upon you for shortening the prayer, [especially] if you fear that those who disbelieve may disrupt [or attack] you. Indeed, the disbelievers are ever to you a clear enemy.
(And when ye go forth in the land) when you travel, (it is no sin for you to curtail (your) worship) curtail the prayer that a sedentary Muslim would usually perform (if ye fear) if you know (that those who disbelieve may attack you) may kill you while in prayer. (In truth the disbelievers are an open enemy to you) this is what is called the prayer of fear (salat al-khawf).