Musnad Ahmad 30:938

Bahz narrated to us, Sulaym—meaning Ibn Hayyan—narrated to us, Sa'id—meaning Ibn Mina—narrated to us, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The change in the breath of the fasting person is more pleasant to Allah on the Day of Resurrection than the scent of musk."