Sunan Ibn Majah Book 7, Hadith 1638

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو مُعَاوِيَةَ، وَوَكِيعٌ، عَنِ الأَعْمَشِ، عَنْ أَبِي صَالِحٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ: قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏ "‏ كُلُّ عَمَلِ ابْنِ آدَمَ يُضَاعَفُ الْحَسَنَةُ بِعَشْرِ أَمْثَالِهَا إِلَى سَبْعِمِائَةِ ضِعْفٍ إِلَى مَا شَاءَ اللَّهُ. يَقُولُ اللَّهُ: إِلاَّ الصَّوْمَ فَإِنَّهُ لِي وَأَنَا أَجْزِي بِهِ. يَدَعُ شَهْوَتَهُ وَطَعَامَهُ مِنْ أَجْلِي. لِلصَّائِمِ فَرْحَتَانِ: فَرْحَةٌ عِنْدَ فِطْرِهِ وَفَرْحَةٌ عِنْدَ لِقَاءِ رَبِّهِ. وَلَخُلُوفُ فَمِ الصَّائِمِ أَطْيَبُ عِنْدَ اللَّهِ مِنْ رِيحِ الْمِسْكِ ‏"‏ ‏.‏

It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) said:“Every good deed of the son of Adam will be multiplied manifold. A good deed will be multiplied ten times up to as many as seven hundred times, or as much as Allah wills. Allah says: ‘Except for fasting, which is for Me and I shall reward for it. He gives up his desire and his food for My sake.’ The fasting person has two joys, one when he breaks his fast and another when he meets his Lord. The smell that comes from the mouth of a fasting person is better before Allah than the fragrance of musk.”