Musannaf Ibn Abi Shayba 22:81

Muhammad ibn Abd Allah al-Asadi narrated to us, from Burayd ibn Abd Allah, from Abu Burdah, from Abu Musa, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Maintain the Quran, for by the One in whose hand is my soul, it is more prone to escaping from the hearts of men than camels from their hobbles."