Musnad Ahmad 30:2240

'Affan narrated to us, 'Abd al-Warith narrated to us, 'Ali ibn Zayd informed us, from Sa'id ibn al-Musayyib, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "Indeed, your Lord, Mighty and Majestic is He, says: 'O son of Adam, for every good deed there are ten good deeds, up to seven hundred times, up to many multiples. And fasting is for Me, and I reward for it. And fasting is a shield from the Fire.'" "And the change in the breath of the mouth of the fasting person is more pleasant to Allah, Mighty and Majestic is He, than the scent of musk. And if an ignorant person acts ignorantly toward one of you while he is fasting, let him say: 'I am fasting.'"