عَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ يَبْلُغُ بِهِ إِلَى النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ إِذَا دُعِيَ أَحَدُكُمْ إِلَى طَعَامٍ وَهُوَ صَائِمٌ فَلْيَقُلْ إِنِّي صَائِمٌ
It is narrated from Sayyiduna Abu Hurairah, may Allah be pleased with him, that the Noble Prophet, peace and blessings be upon him, said: When any of you is invited and he is fasting, then he should say that he is fasting.