Yahya related to me from Malik from Nafi from Abdullah ibn Umarthat the Messenger of Allah, may Allah bless him and grant him peace,said, "When you are invited to a wedding feast, you must go to it." (RU)
USC-MSA web (English) reference: Book 28, Hadith 49 (RU)
Arabic reference (RU): Book 28, Hadith 1144 (RU)