Sayyiduna Abu Hurairah (may Allah be pleased with him) narrated from the Messenger of Allah (peace and blessings be upon him), he (peace be upon him) said: "On the Day of Resurrection, the smell from the mouth of the fasting person will be better with Allah than the fragrance of musk."
Hadith Referenceمسند اسحاق بن راهويه / كتاب الصوم / 419
Hadith Takhrij«بخاري ، كتاب التوحيد ، باب ذكر النبيؑ الخ ، رقم : 7538 . مسلم ، كتاب الصيام ، باب فضل الصيام ، رقم : 1151 . سنن نسائي ، رقم : 2211 . مسند احمد : 393/2»
Explanation & Benefits
Hafiz Abdush Shakoor Tirmidhi
Benefits: The odor (khaluf) should be due to abstaining from eating and drinking for a considerable period, not because of neglecting the use of the tooth-stick (miswak). This odor will be more fragrant to Allah than the scent of musk on the Day of Resurrection. From this, the virtue of the fasting person and the reward and recompense for enduring hunger and thirst are understood.