Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said:

لَيْسَ الْغِنَى عَنْ كَثْرَةِ الْعَرَضِ وَلَكِنَّ الْغِنَى غِنَى النَّفْسِ

Wealth is not in having many possessions. Rather, true wealth is the richness of the soul.

Source: Sahih al-Bukhari