The Messenger of Allah ﷺ said, "By Him in whose hand is the soul of Muhammad, the smell of the fasting person's mouth is sweeter to Allah than the fragrance of musk. He leaves aside his desire, his food, and his drink for My sake. Fasting is Mine, and I Myself reward it."
وقال رسول الله ﷺ والذي نفس محمد بيده لخلوف فم الصائم أطيب عند الله من ريح المسك يذر شهوته وطعامه وشرابه من جراي فالصيام لي وأنا أجزي به
This is also sahih, and its beginning is from the words of the Prophet ﷺ, while the rest of it, starting from his saying "he sowed his desire," is a divine hadith (hadith qudsi), as is apparent, even though this is not explicitly stated in this particular narration. It is found in the individual manuscript (Sahifah) under number 16, and the two Shaykhs did not narrate it through this route, but through other routes, with similar wording. Bukhari narrated it as part of a longer hadith, 7:4-91 Fath, through the route of the Aaraj recension, and Muslim narrated its meaning in scattered form across several hadiths, through various routes, 1:316-317 Bulaq. It will also come in two hadiths through the route of the Aaraj recension, numbers 9999 and 10000. It has also previously appeared through another route in a longer hadith narrated by Abu Salih from Abu Hurairah, number 7679, and its meanings have appeared scattered across many narrations, including numbers 7596, 7775, and 8043-8045.