Sayyiduna Abu Umamah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) said: "Fasting is a shield, and it is one of the fortresses of the believer. Every deed belongs to the one who does it, but fasting is for Me, and I Myself shall reward it."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7577