Musnad Ahmad 30:489

'Abd al-Razzaq narrated to us, Sufyan informed us, from al-A'mash, from Dhakwan, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Every good deed the son of Adam performs is multiplied tenfold, up to seven hundred times, except for fasting. For it is Mine, and I reward for it. He leaves his desire for My sake, and he leaves his food for My sake." "There are two joys for the fasting person: a joy at the time of his breaking his fast, and a joy at the time of meeting his Lord, the Almighty and Majestic." "And the change in the breath of the mouth of the fasting person is more pleasant to Allah than the scent of musk."