Musnad Ahmad 27:218

Yahya narrated to us, from Ubaydullah, Nafi’ informed me, from Ibn Umar, from the Prophet (peace and blessings of Allah be upon him), who said: "The example of the companion of the Quran is like the example of the owner of hobbled camels; if he keeps them tied, he retains them, and if he lets them go, they go away."