It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that the Holy Prophet (peace and blessings of Allah be upon him) said: Allah Almighty has said, "Every deed of the son of Adam is an expiation except for fasting; fasting is exclusively for Me and I Myself will reward for it. The breath of the fasting person is more pleasant to Allah than the fragrance of musk."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 10554