It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "The example of the companion of the Qur'an is like that of a camel with its knee tied. If he (the companion of the Qur'an) keeps firm hold of it, he will be able to restrain it, and if he lets it loose, it will quickly go away."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4051