Sunan Ibn Majah, Volume 3, Book 9, Hadith 1914 (DarusSalam) ⓘ
It was narrated from Ibn 'Umar: that the Messenger of Allah said: “If anyone of you is invited to a wedding feast, let him accept.”
حَدَّثَنَا إِسْحَاقُ بْنُ مَنْصُورٍ، أَنْبَأَنَا عَبْدُ اللَّهِ بْنُ نُمَيْرٍ، حَدَّثَنَا عُبَيْدُ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ قَالَ " إِذَا دُعِيَ أَحَدُكُمْ إِلَى وَلِيمَةِ عُرْسٍ فَلْيُجِبْ " .
also referenced under: Hadith 1914 (Reference) & Book 9, Hadith 1989 (In-Book)