Hadith 3484
Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates: I heard the Prophet Muhammad (peace and blessings be upon him) saying: "If any of you is insulted while he is fasting, he should say: 'I am fasting.'" (The narrator states:) The Prophet Muhammad (peace and blessings be upon him) forbade, through this, that the fasting person should respond to the one who insults him.