Musnad Abu Ya'la al-Mawsili 155:107

On the authority of Abu Hurayrah, he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Every deed of the son of Adam has a good deed [multiplied] by ten times its like, up to seven hundred times, except for fasting. For it is Mine, and I reward for it. He leaves his food and his desire, and he leaves his drink for his desire, for My sake. It is Mine, and I reward for it."