"The Prophet (peace be upon him) said; "Allah has said; 'All the deeds of Adam's children (all mankind) they do for themselves, except fasting which belongs to Me and I will reward for it. Fasting is a shield (against the Hell and against the committing of sins). If one of you happens to be fasting he should avoid sexual relations with his wife and should avoid quarrelling. Should someone fight or quarrel with him, let him say, 'I am fasting'. By Him in Whose Hand is my soul (Allah), the smell of the mouth of the one who is fasting is better in the sight of Allah than musk (perfume)."
[from the collection of sayings of the Prophet by Imam Bukhari]