Musnad Ahmad 27:866

I read to Abd al-Rahman, [who said] Malik [narrated] from Nafi, from Abdullah 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 like the owner of hobbled camels; if he remains attentive to them, he keeps them, and if he lets them go, they depart."