An Nisa, 101 Ayah
4:101
وَإِذَا ضَرَبۡتُمۡ فِي ٱلۡأَرۡضِ فَلَيۡسَ عَلَيۡكُمۡ جُنَاحٌ أَن تَقۡصُرُواْ مِنَ ٱلصَّلَوٰةِ إِنۡ خِفۡتُمۡ أَن يَفۡتِنَكُمُ ٱلَّذِينَ كَفَرُوٓاْۚ إِنَّ ٱلۡكَٰفِرِينَ كَانُواْ لَكُمۡ عَدُوّٗا مُّبِينٗا ١٠١
Wa 'Idhā Đarabtum Fī Al-'Arđi Falaysa `Alaykum Junāĥun 'An Taqşurū Mina Aş-Şalāati 'In Khiftum 'An Yaftinakumu Al-Ladhīna Kafarū ۚ 'Inna Al-Kāfirīna Kānū Lakum `Adūwāan Mubīnāan
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.