Book 20, Number 20.56.189:

Yahya related to me from Malik from Nafi from Abdullah ibn Umar that Hafsa, umm al-muminin, once said to the Messenger of Allah, may Allah bless him and grant him peace, "Why is it that everyone has left ihram and you still have not left ihram from your umra?" and he replied, "I have matted my hair and garlanded my sacrificial animal and will not leave ihram until I have sacrificed the animal."