Mishkat al-Masabih 7 Fasting كتاب الصوم 120

وَعَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: ” إِذَا دُعِيَ أَحَدُكُمْ إِلَى طَعَامٍ وَهُوَ صَائِمٌ فَلْيَقُلْ: إِنِّي صَائِمٌ ” . وَفِي رِوَايَةٍ قَالَ: «إِذَا دُعِيَ أَحَدُكُمْ فَلْيُجِبْ فَإِنْ كَانَ صَائِمًا فَلْيُصَلِّ وَإِن كَانَ مُفطرا فيطعم» . رَوَاهُ مُسلم

Abu Huraira reported God’s messenger as saying, “When one of you is invited to a meal at a time when he is fasting he should say he is fasting.” In a version he said, “When one of you receives an invitation he should accept it. If he is fasting he should pray, but if not, he should eat.” Muslim transmitted it.