Mishkat al-Masabih 8 The Excellent Qualities of the Qur’an كتاب فضائل القرآن 87

وَعَنِ ابْنِ عُمَرَ قَالَ: نَهَى رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِن يُسَافَرَ بِالْقُرْآنِ إِلَى أَرْضِ الْعَدُوِّ. مُتَّفَقٌ عَلَيْهِ. وَفِي رِوَايَةٍ لِمُسْلِمٍ: «لَا تُسَافِرُوا بِالْقُرْآنِ فَإِنِّي لَا آمن أَن يَنَالهُ الْعَدو»

Ibn ‘Umar said that God’s-messenger forbade taking the Qur’ān into enemy territory. A version by Muslim has, “Do not take the Qur’ān with you when travelling, for I cannot guarantee that the enemy will not get it.” (Bukhārī and Muslim.)