Musnad Ahmad 30:3561

Rawh narrated to us, Ibn Jurayj narrated to us, ‘Ata’ informed me, from Abu Salih al-Zayyat, that he heard Abu Hurayrah saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Every deed of the son of Adam is for him, except for fasting; for it is Mine, and I shall reward for it. By the One in Whose hand is my soul, the change in the breath of the mouth of the fasting person is more pleasant to Allah on the Day of Resurrection than the scent of musk. Fasting is a shield. And for the fasting person, there are two joys that he rejoices in: when he breaks his fast, he rejoices in his breaking of the fast, and when he meets his Lord, the Mighty and Majestic, he rejoices in his fasting."