Sahih Muslim 1051
Sahih Muslim · Book 12: The Book of Zakat · The virtue of contentment and encouragement thereof
Abu Huraira reported that the Messenger of Allah (ﷺ) had said:
حَدَّثَنَا زُهَيْرُ بْنُ حَرْبٍ ، وَابْنُ، نُمَيْرٍ قَالاَ حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ ، عَنْ أَبِي الزِّنَادِ ، عَنِ الأَعْرَجِ ، عَنْ أَبِي هُرَيْرَةَ ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لَيْسَ الْغِنَى عَنْ كَثْرَةِ الْعَرَضِ وَلَكِنَّ الْغِنَى غِنَى النَّفْسِ " .
Richness does not lie in the abundance of (worldly) goods but richness is the richness of the soul (heart, self).