Sahih Al Bukhari – Book of Dress
Volumn 007, Book 072, Hadith Number 811.
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Narated By Abu Huraira RA: The Prophet PBUH said, "(Allah said), 'Every good deed of Adam's son is for him except fasting; it is for Me. and I shall reward (the fasting person) for it.' Verily, the smell of the mouth of a fasting person is better to Allah than the smell of musk."