Allah the Exalted and Majestic said: Every act of the son of Adam is for him, except fasting. It is (exclusively) meant for Me and I (alone) will reward it. Fasting is a shield. When any one of you is fasting on a day, he should neither indulge in obscene language, nor raise the voice; or if anyone reviles him or tries to quarrel with him he should say: I am a person fasting. By Him, in Whose Hand is the life of Muhammad, the breath of the observer of fast is sweeter to Allah on the Day of judgment than the fragrance of musk. The one who fasts has two (occasions) of joy, one when he breaks the fast he is glad with the breaking of (the fast) and one when he meets his Lord he is glad with his fast.
The Exclusive Reward of Fasting
All acts of worship have their prescribed rewards, but fasting holds a unique status. Allah declares it exclusively for Himself, indicating a special, intimate connection and a reward beyond measure that He alone knows and bestows.
Fasting as a Spiritual Shield
The fast is described as a "shield" (junnah). It protects the believer from sins, evil speech, and the temptations of the lower self (nafs). It is a spiritual armor that guards one's faith and piety.
The Etiquette of the Fasting Person
The true fast is not merely abstaining from food and drink. One must also restrain the tongue from foul language, arguments, and idle talk. If provoked, the believer should simply state, "I am fasting," reminding themselves and others of their sacred state.
The Divine Fragrance
Allah swears by His Own Essence that the breath of the fasting person is more beloved to Him than the scent of musk. This signifies the immense honor and love Allah has for this act of worship, transforming even a physical sign of hardship into something precious.
The Two Joys
The fasting person experiences two distinct joys: the immediate, permissible joy of breaking the fast (iftar), and the ultimate, everlasting joy of meeting his Lord and receiving the full reward for his fast on the Day of Judgment.
This hadith is found in Sahih Muslim, The Book of Fasting, Hadith Number: 1151 d.