From Sahih Bukhari (Hadith 1566):
Narrated Ibn `Umar:Hafsa the wife of the Prophet (ﷺ) said, "O Allah's Messenger (ﷺ)! Why have the people finished their Ihram after performing `Umra but you have not finished your Ihram after performing `Umra?" He replied, "I have matted my hair and garlanded my Hadi. So I will not finish my Ihram till I have slaughtered (my Hadi)
Reference: Bukhari 1566