1
إِذَا دُعِيَ أَحَدُكُمْ فَلْيُجِبْ, فَإِنْ كَانَ صَائِماً فَلْيُصَلِّ, وَإِنْ كَانَ مُفْطِراً فَلْيَطْعَمْ, وَمَعْنَى فَلْيُصَلِّ أَيْ فَلْيَدْعُ.
(If you are not invited (to a meal) then answer. If you happen to be fasting, then supplicate (for those present) and if you are not fasting, then eat.)
Source: Muslim 2/1054.