Allah said, "Fasting is for Me, and I Myself reward it." The fasting person has two moments of joy, one when he meets his Lord and one when he breaks his fast. The smell of the fasting person's breath is more pleasing to Allah than the fragrance of musk.
أخبرنا محمد بن بشار قال حدثنا محمد قال حدثنا شعبة عن أبي إسحق عن أبي الأحوص قال
الله عز وجل الصوم لي وأنا أجزي به وللصائم فرحتان فرحة حين يلقى ربه وفرحة عند إفطاره ولخلوف فم الصائم أطيب عند الله من ريح المسك
Its isnad is sahih, and it is in Kubra, hadith no. 2522. Tabarani also narrated it in Kabir, 10/120, hadith no. 10078, with a sahih isnad from Shubah with the same wording, marfu. So the hadith is sahih both as marfu and mawquf. See the previous hadith.