Musnad Ahmad 203:3

Waki' narrated to us, he said: My father and Isra'il narrated to us, from Abu Ishaq, from Abu al-Ahwas, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do you have any wealth?" He said: I said: "Yes, from every kind of wealth Allah the Almighty has given me: from camels, horses, and slaves." He said: "If Allah the Almighty gives you wealth, then let the effect of it be seen upon you."