The Messenger of Allah ﷺ forbade traveling with the Quran into enemy territory.Malik said, "This is only out of fear that the enemy might get hold of it."
نهى رسول الله ﷺ أن يسافر بالقرآن إلى أرض العدو. قال مالك: وإنما ذلك مخافة أن يناله العدو.
Malik related it in Jihad (6) from Nafi, from Abdullah bin Umar, and mentioned it. Bukhari related it in Jihad and Sayr (2990), and Muslim in Imarah (1869), both from the hadith of Malik with his chain, in similar wording.As for Malik's statement, "This is only out of fear that the enemy might get hold of it," most of the narrators from Malik attributed this explanation to him and did not raise it to the level of the Prophet's own words. Ibn Wahb alone raised it to that level, as Ibn Hajar stated, and it has indeed been confirmed as such from a source other than Malik.Layth bin Saad raised it, narrating from Nafi, with the wording, "The Prophet ﷺ used to forbid traveling with the Quran into enemy territory, out of fear that the enemy might get hold of it." Muslim related this from Qutayba, who said, Layth narrated to us.Ayub also raised it, narrating from Nafi, with the wording, "Do not travel with the Quran, for I cannot be certain that the enemy will not get hold of it." Muslim related this through several routes from Hammad, from Ayub.It may be that Malik was uncertain whether this statement should be attributed to the Prophet, and so he presented it as his own.