Musnad Ahmad 32:661

Yahya ibn Ishaq narrated to us, Mahdi narrated to us, Ghaylan ibn Jarir narrated to me, from Anas ibn Malik, who said: "Indeed, you perform deeds that are finer in your eyes than a hair, [yet] we used to count them, during the time of the Messenger of Allah (peace and blessings of Allah be upon him), among the destructive sins."