Musnad Ahmad 1155:14

Abu al-Yaman narrated to us, Shu'ayb—meaning ibn Abi Hamzah—narrated to us, he said: Nafi' said: Abdullah ibn Umar used to say: Hafsa, the wife of the Prophet, may God bless him and grant him peace, informed me that the Prophet, may God bless him and grant him peace, commanded his wives to exit the state of ihram during the year of the Farewell Pilgrimage. So a certain woman said to him: "What prevents you from exiting the state of ihram?" He said: "I have matted my hair with gum, and I have garlanded my sacrificial animal, so I will not exit the state of ihram until I slaughter my sacrificial animal."