Nafi' narrates from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) forbade "travelling with the Qur'an to the land of the enemy."
Imam Malik (may Allah have mercy on him) said: I think it was out of fear that the enemy might get hold of it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18239