The Prophet ﷺ said, "Wealth is not in the abundance of possessions, but true wealth is the richness of the soul."
عن النبي ﷺ قال: ليس الغنى عن كثرة العرض، ولكن الغنى غنى النفس.
Bukhari narrated it in Riqaq (6446), and Muslim in Zakat (1051), both through chains from Abu Hurairah, who mentioned it. The meaning of the richness of the soul is that it has no greed for, or inclination toward, what is in people's hands.