Musnad Ahmad 32:1434

Yunus narrated to us, Hammad—meaning Ibn 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, hold a wedding feast for any of his wives as he held for Zaynab bint Jahsh." He said: "He held a feast with a sheep, or he slaughtered a sheep."