It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: Fasting is a shield. When any one of you is observing a fast, he should neither indulge in indecent talk nor act ignorantly. If someone tries to fight or abuse him, he should simply say: I am fasting.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 9947