Allah, the Exalted and Majestic, said: Fast (is exclusively) meant for Me and I would give its reward. There are two (occasions) of joy for the observer of fast. He feels joy when he breaks the fast and he is happy when he meets Allah. By Allah in Whose Hand is the life of Muhammad, the breath of the observer of fast is sweeter to Allah than the fragrance of musk.
The Book of Fasting - Sahih Muslim 1151 f
Allah, the Exalted and Majestic, said: Fast (is exclusively) meant for Me and I would give its reward. There are two (occasions) of joy for the observer of fast. He feels joy when he breaks the fast and he is happy when he meets Allah. By Allah in Whose Hand is the life of Muhammad, the breath of the observer of fast is sweeter to Allah than the fragrance of musk.
Scholarly Commentary
This sacred Hadith Qudsi reveals the exceptional status of fasting among acts of worship. When Allah declares "Fast is exclusively meant for Me," this signifies that fasting is a purely hidden act between the servant and his Lord, unlike prayer or charity which may be witnessed by others.
The divine promise "I would give its reward" indicates that Allah Himself will recompense the fasting person without measure, as the reward is not specified like other acts of worship, demonstrating Allah's boundless generosity.
The two joys mentioned represent both worldly and spiritual happiness: the legitimate pleasure of breaking one's fast after abstaining, and the eternal joy of meeting Allah while having fulfilled this noble obligation.
The comparison of the fasting person's breath to musk, despite its physical unpleasantness, shows how Allah transforms the struggles of His servants into something beloved to Him, elevating their spiritual state above physical appearances.