Musnad Ahmad 30:2152

'Affan narrated to us, he said: Sulaym narrated to us, he said: Sa'id narrated to us, he said: I heard Abu Hurayrah saying: The Messenger of Allah, peace and blessings of Allah be upon him, said: "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."