Abu Hurayrah and Abu Sa'id (may Allah be pleased with them both) both narrate that the Messenger of Allah (peace and blessings be upon him) said: "Allah says: Fasting is for Me and I will give its reward. The fasting person has two joys: when he breaks his fast he rejoices, and when he meets his Lord, His reward will make him rejoice. And the smell of the fasting person's mouth is more beloved to Allah Almighty than musk."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8333