Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: Allah, the Mighty and Majestic, said: "Every deed of the son of Adam is for him except fasting; it is for Me, and I Myself will reward it. Fasting is a shield. So when it is the day of fasting for one of you, he should not engage in obscenity on that day, nor shout abusively. If someone abuses him or fights him, let him say: 'I am a fasting person.' By the One in whose Hand is the soul of Muhammad (peace and blessings be upon him), the smell of the fasting person's mouth will be more pleasant to Allah Almighty on the Day of Resurrection than the fragrance of musk. The fasting person has two joys: when he breaks his fast he rejoices, and when he meets his Lord he will rejoice because of his fasting."
(In the hadith of Hisham, at the beginning, it says that Allah Almighty says: "Every deed of the son of Adam is for him.")
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8310