(24) باب النَّهْىِ أَنْ يُسَافَرَ بِالْمُصْحَفِ إِلَى أَرْضِ الْكُفَّارِ إِذَا خِيفَ وُقُوعُهُ بِأَيْدِيهِمْ
It has been narrated on the authority of Abdullah b. Umar that the Messenger of Allah (ﷺ) 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.
Reference: Sahih Muslim 1869 b
In-book reference: Book 33, Hadith 136
USC-MSA web (English) reference(deprecated numbering scheme): Book 20, Hadith 4608