Musnad Ahmad 30:575

'Abd al-Razzaq and Ibn Bakr narrated to us, they said: Ibn Jurayj informed us, 'Ata' informed me, from Abu Salih al-Zayyat, that he heard Abu Hurayrah saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Every deed of the son of Adam is for him, except for fasting; for it is Mine, and I shall reward for it." "Fasting is a shield. When it is the day of fasting for one of you, he should not use obscene language on that day, nor should he shout. If someone insults him or fights him, let him say: 'I am a fasting person,' twice." "By the One in Whose hand is the soul of Muhammad, the change in the breath of the fasting person is more pleasant to Allah on the Day of Resurrection than the scent of musk." "And the fasting person has two joys that he rejoices in: when he breaks his fast, he rejoices in his breaking of the fast, and when he meets his Lord, the Mighty and Majestic, he rejoices in his fasting."