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. Sahih Muslim 1869 c

Arabic hadith text
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 ‏.‏
Translation
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.