Abü Hurairah [may Allah be pleased with them] said: “The Messenger of Allah صَلَّ اللهُ عَلَيْهِ وَ سَلَّمُ said: ‘Allah, the Most High, said: “Every deed of the son of Adam is for him, except fasting. It is for Me, and I shall reward for it.” Fasting is a shield, so when it is a day when one of you is fasting, let him not utter any obscene speech that day nor raise his voice. If anyone reviles him, or argues with him, let him say: “I am a man who is fasting, I am fasting.” By the One in Whose Hand is the soul of Muhammad! The smell of the mouth of the fasting person will be better to Allah on the Day of Resurrection than the fragrance of musk. The fasting person has two moments of joy that he rejoices in: When he breaks his fast he rejoices at breaking his fast, and when he meets his Lord he will rejoice in his fasting.”
Sahih Muslim, Vol. 3 [2761, 163].