Musnad Ahmad 30:3560

Rawh narrated to us, Hisham narrated to us, from Muhammad, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "A good deed is [rewarded] by ten times its like. And fasting is for Me, and I reward for it; he leaves his food and his drink for My sake, so fasting is for Me and I reward for it." "And the change in the breath of the fasting person is more pleasant to Allah than the scent of musk."