It was narrated from Abu Hurairah that the Prophet (ﷺ) said (that Allah said):"For every good deed that the son of Adam does, he will have (the reward of) ten the like thereof, except for fasting. It is for Me and I shall reward for it.
أَخْبَرَنَا أَحْمَدُ بْنُ عِيسَى، قَالَ حَدَّثَنَا ابْنُ وَهْبٍ، عَنْ عَمْرٍو، عَنْ بُكَيْرٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " كُلُّ حَسَنَةٍ يَعْمَلُهَا ابْنُ آدَمَ فَلَهُ عَشْرُ أَمْثَالِهَا إِلاَّ الصِّيَامَ لِي وَأَنَا أَجْزِي بِهِ " .
Nesai
The Book of Fasting • Hadith 2219