It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: When any one of you is fasting on any day, he should neither speak indecently nor act ignorantly. If someone behaves ignorantly towards him, he should say, "I am fasting."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 7840