Musnad Ahmad 25:1269

Hushaym narrated to us, Yazid ibn Abi Ziyad informed us, from Mujahid, from Ibn Abbas, that he said: "The Prophet, may Allah bless him and grant him peace, entered into the state of Ihram for Hajj. When he arrived, he performed Tawaf around the House (the Kaaba) and between al-Safa and al-Marwah, but he did not shorten his hair and did not exit the state of Ihram because of the sacrificial animal (Hady). He commanded those who had not brought the sacrificial animal to perform Tawaf, to perform Sa'i, and to shorten or shave their hair, and then to exit the state of Ihram."