Musnad Abu Ya'la al-Mawsili 159:11

Abu Khaythama narrated to us, Sufyan narrated to us, from Abu al-Zinad, from al-A'raj, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Wealth is not [derived] from the abundance of worldly goods, but rather, true wealth is the wealth of the soul."