I heard the Messenger of Allah ﷺ say, "Allah said, 'Every deed of the son of Adam is for him, except fasting. It is for Me, and I shall reward it. By the One in whose hand is the soul of Muhammad, the breath of the fasting person is more fragrant to Allah than the scent of musk.'"
أخبرنا الربيع بن سليمان قال حدثنا ابن وهب قال أخبرني يونس عن ابن شهاب قال حدثني سعيد بن المسيب أن
سمعت رسول الله ﷺ يقول قال الله عز وجل كل عمل ابن آدم له إلا الصيام هو لي وأنا أجزي به والذي نفس محمد بيده لخلفة فم الصائم أطيب عند الله من ريح المسك
Muslim narrated it, hadith: 161/1151 (see the earlier hadith, hadith: 2217), from the hadith of Abdullah bin Wahb, and Bukhari, in the Book of Clothing, chapter on what is mentioned about musk, hadith: 5927, from the hadith of Ibn Shihab Zuhri, with this wording, and it is in Kubra, hadith: 2528.