It is narrated from Hazrat Abu Hurairah (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: When any of you is fasting on a certain day, he should not behave indecently nor act ignorantly. If someone behaves ignorantly towards him, he should say, "I am fasting."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 8674