Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) and others narrate from the Prophet (peace and blessings be upon him): "Whenever one of you is invited to a wedding feast (walimah), let him accept," and he (peace and blessings be upon him) did not specify three days or anything else.
Al-Bukhari said about the hadith of Zuhayr bin Uthman: Its chain is not authentic, and he is not known to have been a Companion; and this (hadith of Ibn Umar) is more authentic.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14514