Foods (Kitab Al-At'imah)
28/1. Chapter:
What has been reported about accepting invitations
Sunan Abi Dawud
حَدَّثَنَا مَخْلَدُ بْنُ خَالِدٍ، حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ عُبَيْدِ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم بِمَعْنَاهُ زَادَ " فَإِنْ كَانَ مُفْطِرًا فَلْيَطْعَمْ وَإِنْ كَانَ صَائِمًا فَلْيَدْعُ " .
The tradition mentioned above has also been transmitted by Ibn ‘Umar to the same effect through a different chain of narrators. This version has the additional words: If he is not fasting, he should eat, and if he is fasting, he should leave it.
Reference : Sunan Abi Dawud 3737In-book reference : Book 28, Hadith 2English translation : Book 27, Hadith 3728