It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) forbade taking the Qur'an along when traveling to the enemy's territory, because there is a fear that it might fall into the hands of the enemy.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 5170
Hadith Gradingحکم دارالسلام:إسناده صحيح ، م : 1869 .