If a fasting person is invited to eat and he does not want to break his fast, or someone insults him or argues with him, it is recommended for him to say: "I am Fasting", and he should protect his fast from obscene speech, ignorance and the like

Sahih Muslim · Book 13 · Hadith 1150

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَعَمْرٌو النَّاقِدُ، وَزُهَيْرُ بْنُ حَرْبٍ، قَالُوا حَدَّثَنَا سُفْيَانُ، بْنُ عُيَيْنَةَ عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، - رضى الله عنه - قَالَ أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ رِوَايَةً وَقَالَ عَمْرٌو يَبْلُغُ بِهِ النَّبِيَّ صلى الله عليه وسلم وَقَالَ زُهَيْرٌ عَنِ النَّبِيِّ ص…

Abu Huraira (Allah be pleased with him) reported Allah's Messenger (ﷺ) as saying: If any one of you is invited to a meal when he is fasting, he should say:" I am fasting."