The Prophet ﷺ said, "The breath of one who is fasting is more fragrant to Allah on the Day of Resurrection than the scent of musk."
حدثنا عبد الله بن الحارث حدثنا داود بن قيس عن موسى بن يسار
أن النبي ﷺ قال خلوف فم الصائم أطيب عند الله يوم القيامة من ريح المسك
Its isnad is sahih, it has previously appeared at 2/395, 407, 461, 462, 465, 467, 475, 477.