“If anyone of you is invited to eat when he is fasting, let him say: ‘I am fasting.’”  

عَنِ النَّبِيِّ ﷺ قَالَ إِذَا دُعِيَ أَحَدُكُمْ إِلَى طَعَامٍ وَهُوَ صَائِمٌ فَلْيَقُلْ إِنِّي صَائِمٌ  

“Whoever is invited to eat when he is fasting, let him accept the invitation; and if he wants to let him eat, and if he wants let him not eat.”  

قَالَ رَسُولُ اللَّهِ ﷺ مَنْ دُعِيَ إِلَى طَعَامٍ وَهُوَ صَائِمٌ فَلْيُجِبْ فَإِنْ شَاءَ طَعِمَ وَإِنْ شَاءَ تَرَكَ