Musnad Ahmad 27:1464

Ishaq ibn Isa narrated to us, Malik informed us, from Nafi, from Ibn Umar, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The likeness of the companion of the Quran is only like the owner of hobbled camels; if he tends to them regularly, he keeps them, and if he lets them loose, they go away."