Musnad Ahmad 30:2137

'Affan narrated to us, Hammad narrated to us, from 'Ali ibn Zayd, from Aws ibn Khalid, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The likeness of the one who hears wisdom and follows the worst of what he hears is like the likeness of a man who came to a shepherd and said to him: 'Slaughter a sheep for me from your flock.' He said: 'Go and take the best sheep by its ear.' So he went and took the sheepdog by its ear."