Sunan at-Tirmithiy كتاب الصوم باب ما جاء فى فضل الصوم

حَدَّثَنَا عِمْرَانُ بْنُ مُوسَى الْقَزَّازُ حَدَّثَنَا عَبْدُ الْوَارِثِ بْنُ سَعِيدٍ حَدَّثَنَا عَلِىُّ بْنُ زَيْدٍ عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ عَنْ أَبِى هُرَيْرَةَ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِنَّ رَبَّكُمْ يَقُولُ كُلُّ حَسَنَةٍ بِعَشْرِ أَمْثَالِهَا إِلَى سَبْعِمِائَةِ ضِعْفٍ وَالصَّوْمُ لِى وَأَنَا أَجْزِى بِهِ الصَّوْمُ جُنَّةٌ مِنَ النَّارِ وَلَخُلُوفُ فَمِ الصَّائِمِ أَطْيَبُ عِنْدَ اللَّهِ مِنْ رِيحِ الْمِسْكِ وَإِنْ جَهِلَ عَلَى أَحَدِكُمْ جَاهِلٌ وَهُوَ صَائِمٌ فَلْيَقُلْ إِنِّى صَائِمٌ. وَفِى الْبَابِ عَنْ مُعَاذِ بْنِ جَبَلٍ وَسَهْلِ بْنِ سَعْدٍ وَكَعْبِ بْنِ عُجْرَةَ وَسَلاَمَةَ بْنِ قَيْصَرٍ وَبَشِيرِ ابْنِ الْخَصَاصِيَةِ. وَاسْمُ بَشِيرٍ زَحْمُ بْنُ مَعْبَدٍ وَالْخَصَاصِيَةُ هِىَ أُمُّهُ. قَالَ أَبُو عِيسَى وَحَدِيثُ أَبِى هُرَيْرَةَ حَدِيثٌ حَسَنٌ غَرِيبٌ مِنْ هَذَا الْوَجْهِ.
The Messenger of God, peace and blessings of God be upon him, said, "Indeed, your Lord says, 'The recorded merit of each righteous deed is worth that of ten like deeds, [or can be multiplied] up to seven hundred times. Fasting is for Me, and I reward it accordingly (1).' Fasting is a shield from Hellfire, and indeed, the breath of a fasting person (2) is more pleasant to God than the scent of musk. If an ignorant person provokes you while you are fasting, respond by saying, 'Indeed, I am fasting.'"
(1) Among the interpretations of this is that unlike other acts of worship, fasting does not have any outwardly apparent rituals, and therefore, cannot be done for show. Only God knows if a person is truly fasting and, in this sense, one fasts in the hope of pleasing God and God alone. Another interpretation is that only God knows the degree of reward and its multiplication for fasting, whereas He has given some indication of the degree of reward for other righteous deeds. (2) As a result of him/her having abstained from eating or drinking for some time.