Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Fasting is a shield. When one of you is fasting, he should not engage in obscenity or ignorant behaviour. If someone fights him or abuses him, let him say: 'I am fasting.'"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8309