Sayyiduna Abu Hurairah, may Allah be pleased with him, narrates this statement of the Prophet Muhammad, peace and blessings be upon him: "Every deed of the son of Adam is for him except fasting; it is different, it is for Me and I will reward it. The smell from the mouth of a fasting person is purer to Allah than the fragrance of musk."
Hadith Referenceصحیح ابن حبان / كتاب الصوم / 3422
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح: م.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط الشيخين