Hadith 1240
Abu Hurairah (May Allah be pleased with him) reported:
عن أبي هريرة رضي الله عنه قال: قال رسول الله صلى الله عليه وسلم: "إذا كان يوم صوم أحدكم فلا يرفث ولا يصخب، فإن سابه أحد أو قاتله، فليقل: إني صائم"
The Messenger of Allah (ﷺ) said, "When any one of you is observing Saum (fasting) on a day, he should neither indulge in obscene language nor should he raise the voice; and if anyone reviles him or tries to quarrel with him he should say: 'I am observing fast."' [Al-Bukhari and Muslim].
In plain words
While fasting, a person should avoid foul speech and quarrels, and if someone provokes them, simply answer that they are fasting. The fast trains character, not just appetite.
Reference : Riyad as-Salihin 1240 In-book reference : Book 8, Hadith 250