Musnad Abu Ya'la al-Mawsili 117:190

Ishaq narrated to us, Hammad bin Zayd narrated to us, from Thabit, from Anas, who said: I did not see the Messenger of Allah (may Allah bless him and grant him peace) give a wedding feast for any of his wives as he gave for Zaynab, for he slaughtered a sheep.