Sahih al-Bukhari, Volume 7, Book 62, Hadith 102 (USC-MSA) ⓘ
Narrated `Abdullah bin `Umar: Allah's Messenger said, "If anyone of you is invited to a wedding banquet, he must go for it (accept the invitation)."
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " إِذَا دُعِيَ أَحَدُكُمْ إِلَى الْوَلِيمَةِ فَلْيَأْتِهَا " .
also referenced under: Book 67, Hadith 108 (In-Book) & Hadith 5173 (DarusSalam)