Musnad Ahmad 1155:2

Yahya ibn Sa'id narrated to us, from 'Ubayd Allah, who said: Nafi' narrated to me, from Ibn 'Umar, from Hafsah, who said: I said, "O Messenger of Allah, what is the matter with the people? They have exited the state of ihram for their 'Umrah, but you have not exited it?" He said, "I have garlanded my sacrificial animal and matted my hair, so I will not exit the state of ihram until I exit it from the Hajj."