The Messenger of Allah ﷺ said, "Every deed of the son of Adam is multiplied, a good deed by ten times its like up to seven hundred times, as much as Allah wills. Allah says, 'Except for fasting, for it is Mine and I Myself reward it. He gives up his desire and his food for My sake.' The fasting person has two joys, a joy when he breaks his fast and a joy when he meets his Lord. And the breath of the fasting person is more fragrant to Allah than the scent of musk."
حدثنا أبو بكر بن أبي شيبة حدثنا أبو معاوية ووكيع عن الأعمش عن أبي صالح
قال رسول الله ﷺ كل عمل ابن آدم يضاعف الحسنة بعشر أمثالها إلى سبع مائة ضعف ما شاء الله يقول الله إلا الصوم فإنه لي وأنا أجزي به يدع شهوته وطعامه من أجلي للصائم فرحتان فرحة عند فطره وفرحة عند لقاء ربه ولخلوف فم الصائم أطيب عند الله من ريح المسك
Bukhari, Tawhid, chapter, "The saying of Allah Almighty, 'they want to change the words of Allah'," no. 7492, from the hadith of Amash, with it, at length and in brief, and Muslim, Fasting, chapter on the merit of fasting, no. 1151/164, from Abu Bakr bin Abu Shayba, with it, and it has many chains in both of them.