Abu Hurairah (May Allah be pleased with him) reported:
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].
App reference: Book 9, Hadith 250
Arabic/English book reference: Book 9, Hadith 1240