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." (IT)
USC-MSA web (English) reference: Book 28, Hadith 49 (IT)
Arabic reference (IT): Book 28, Hadith 1144 (IT)