Sahih Bukhari Volume 3, Book 30, Hadith 1905

حَدَّثَنَا إِبْرَاهِيمُ بْنُ مُوسَى، أَخْبَرَنَا هِشَامُ بْنُ يُوسُفَ، عَنِ ابْنِ جُرَيْجٍ، قَالَ أَخْبَرَنِي عَطَاءٌ، عَنْ أَبِي صَالِحٍ الزَّيَّاتِ، أَنَّهُ سَمِعَ أَبَا هُرَيْرَةَ ـ رضى الله عنه ـ يَقُولُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ قَالَ اللَّهُ كُلُّ عَمَلِ ابْنِ آدَمَ لَهُ إِلاَّ الصِّيَامَ، فَإِنَّهُ لِي، وَأَنَا أَجْزِي بِهِ‏.‏ وَالصِّيَامُ جُنَّةٌ، وَإِذَا كَانَ يَوْمُ صَوْمِ أَحَدِكُمْ، فَلاَ يَرْفُثْ وَلاَ يَصْخَبْ، فَإِنْ سَابَّهُ أَحَدٌ، أَوْ قَاتَلَهُ فَلْيَقُلْ إِنِّي امْرُؤٌ صَائِمٌ‏.‏ وَالَّذِي نَفْسُ مُحَمَّدٍ بِيَدِهِ لَخُلُوفُ فَمِ الصَّائِمِ أَطْيَبُ عِنْدَ اللَّهِ مِنْ رِيحِ الْمِسْكِ، لِلصَّائِمِ فَرْحَتَانِ يَفْرَحُهُمَا إِذَا أَفْطَرَ فَرِحَ، وَإِذَا لَقِيَ رَبَّهُ فَرِحَ بِصَوْمِهِ ‏"‏‏

Narrated By Abu Huraira : Allah's Apostle said, "Allah said, 'All the deeds of Adam's sons (people) are for them, except fasting which is for Me, and I will give the reward for it.' Fasting is a shield or protection from the fire and from committing sins. If one of you is fasting, he should avoid sexual relation with his wife and quarrelling, and if somebody should fight or quarrel with him, he should say, 'I am fasting.' By Him in Whose Hands my soul is' The unpleasant smell coming out from the mouth of a fasting person is better in the sight of Allah than the smell of musk. There are two pleasures for the fasting person, one at the time of breaking his fast, and the other at the time when he will meet his Lord; then he will be pleased because of his fasting."