Musannaf Ibn Abi Shayba 34:182

'Abd al-Wahhab al-Thaqafi narrated to us, from Yunus, from al-Hasan, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "The wedding feast on the first day is a right, and on the second day it is a kindness, and whatever is beyond that is showing off."