Sahih Muslim Book 20, Hadith Number 4608.

Chapter : It is forbidden to take the Qur’an to the land of the infidels when it is feared that it might fall into their hands.

It has been narrated on the authority of Abdullah b. Umar that the Messenger of Allah (may peace be upon him) used to forbid that one should travel to the land of the enemy taking the Qur’an (with him) lest it should fall into the hands of the enemy.