The Messenger of Allah ﷺ said, "Allah has made every good deed of the son of Adam multiplied tenfold up to seven hundred times, except for fasting. Fasting is for Me, and I Myself shall reward it. The one who fasts has two moments of joy, one when he breaks his fast and one when he meets his Lord on the Day of Resurrection. And the breath of the fasting person is more fragrant to Allah than the scent of musk."
حدثنا عبد الله قال قرأت على أبي حدثكم عمرو بن مجمع أبو المنذر الكندي قال أخبرنا إبراهيم الهجري عن أبي الأحوص
قال رسول الله ﷺ إن الله عز وجل جعل حسنة ابن آدم بعشر أمثالها إلى سبع مائة ضعف إلا الصوم والصوم لي وأنا أجزي به وللصائم فرحتان فرحة عند إفطاره وفرحة يوم القيامة ولخلوف فم الصائم أطيب عند الله من ريح المسك
Its chain is daif because of the weakness of Ibrahim bin Muslim Hijri, as we mentioned at 3623.Amr bin Mujammi ibn Yazid bin Abu Sulayman, Abu Mundhir Sakuni, with fatha on the sin and damma on the kaf, a relation to Sakun, a tribe from Kinda, was mentioned by Ibn Hibban in al-Thiqat, who said, "He makes mistakes." Neither Bukhari nor Nasai mentioned him among the daif narrators, and Ibn Khuzayma graded his hadith sahih, but only as a corroborating narration, as stated in al-Tajil. Ibn Main, Daraqutni, and others graded him daif. Ibn Abu Hatim said in al-Jarh wal-Tadil 3/1/265, "I asked my father about him, and he said, 'His hadith is daif.'" However, he is one of Ahmad's teachers, and we hold the view that Ahmad was careful about his teachers and their hadiths, and was wary of taking from them what they got wrong.The hadith appears in Majma al-Zawaid 3:179-180, where it says, "Ahmad and Bazzar, in abridged form, and Tabarani in al-Kabir narrated it... It has chains of transmission in Tabarani, and some of its routes have narrators who are the narrators of the sahih. In Ahmad's chain is Amr bin Mujammi, who is daif." This is what he said, but in my view, the defect in this chain is Ibrahim Hijri.As for the wording of the hadith, it is firmly established as sahih through the hadith of Abu Hurairah in the two Sahihs and others. See al-Targhib wal-Tarhib 2:57-58.Khuluf, with damma on the kha, means the change in the odor of the mouth. Its origin, in plants, refers to one thing growing after another, because it is a smell that arises after the first smell. This is what Ibn Athir said.