Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said, “Every good deed of the son of Adam is multiplied by ten like it, up to seven hundred more. Allah said: Except for fasting, for it is Mine and I will reward it.”
Source: Ṣaḥīḥ Muslim 1151
Grade: Sahih (authentic) according to Muslim
عَنْ أَبِي هُرَيْرَةَ قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كُلُّ عَمَلِ ابْنِ آدَمَ يُضَاعَفُ الْحَسَنَةُ عَشْرُ أَمْثَالِهَا إِلَى سَبْعِمِائَةِ ضِعْفٍ قَالَ اللهُ إِلَّا الصَّوْمَ فَإِنَّهُ لِي وَأَنَا أَجْزِي بِهِ
1151 صحيح مسلم كتاب الصيام باب فضل الصيام
