Surah An-Nisa' (The Women), Verse 101

وَاِذَا ضَرَبْتُمْ فِی الْاَرْضِ فَلَیْسَ عَلَیْكُمْ جُنَاحٌ اَنْ تَقْصُرُوْا مِنَ الصَّلٰوةِ اِنْ خِفْتُمْ اَنْ یَّفْتِنَكُمُ الَّذِیْنَ كَفَرُوْا اِنَّ الْكٰفِرِیْنَ كَانُوْا لَكُمْ عَدُوًّا مُّبِیْنًا ۟

Wa izaa darabtum fil ardi falaisa 'alaikum junaahun an taqsuroo minas Salaati in khiftum ai yaftinakumul lazeena kafarooo; innal kaafireena kaanoo lakum aduwwam mubeenaa

“When ye travel through the earth, there is no blame on you if ye shorten your prayers, for fear the Unbelievers May attack you: For the Unbelievers are unto you open enemies.”

Quran 4:101 (Yusuf Ali Translation)