كتاب الإمارة
33
The Book on Government
(24)
Chapter: The prohibition of travelling with the Mushaf to the land of the disbelievers if there is the fear that it may fall into their hands.
(24)
باب النَّهْىِ أَنْ يُسَافَرَ بِالْمُصْحَفِ إِلَى أَرْضِ الْكُفَّارِ إِذَا خِيفَ وُقُوعُهُ بِأَيْدِيهِمْ

It has been narrated on the authority of Ibn 'Umar that the Messenger of Allah (ﷺ) said:

Do not take the Qur'an on a journey with you, for I am afraid lost it should fall into the hands of the enemy. Ayyub (one of the narrators in the chain of transmitters) said: The enemy may seize it and may quarrel with you over it.
وَحَدَّثَنَا أَبُو الرَّبِيعِ الْعَتَكِيُّ، وَأَبُو كَامِلٍ قَالاَ حَدَّثَنَا حَمَّادٌ، عَنْ أَيُّوبَ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ لاَ تُسَافِرُوا بِالْقُرْآنِ فَإِنِّي لاَ آمَنُ أَنْ يَنَالَهُ الْعَدُوُّ ‏"‏ ‏.‏ قَالَ أَيُّوبُ فَقَدْ نَالَهُ الْعَدُوُّ وَخَاصَمُوكُمْ بِهِ ‏.‏
Reference : Sahih Muslim 1869 b
In-book reference : Book 33, Hadith 137
USC-MSA web (English) reference : Book 20, Hadith 4609
  (deprecated numbering scheme)