Compiled by Imam Yahya ibn Sharaf al-Nawawi
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].