Musnad Ahmad 25:449

'Affan narrated to us, Khalid narrated to us, Yazid ibn Abi Ziyad narrated to us, from Mujahid, from Ibn 'Abbas, who said: We arrived with the Messenger of Allah (peace and blessings of Allah be upon him) as pilgrims, and he commanded them, so they made it an 'Umrah. Then he said: "If I had faced of my affair what I have turned my back upon, I would have done as they did, but the 'Umrah has entered into the Hajj until the Day of Resurrection." Then he interlaced his fingers with one another. So the people dissolved [their Ihram], except for those who had a sacrificial animal with them. 'Ali arrived from Yemen, and the Messenger of Allah (peace and blessings of Allah be upon him) said to him: "With what did you enter into Ihram?" He said: "I entered into Ihram with what the Prophet entered into Ihram." He said: "Do you have a sacrificial animal with you?" He said: "No." He said: "Then remain as you are, and you have a third of my sacrificial animal." He said: And there was with the Messenger of Allah (peace and blessings of Allah be upon him) one hundred camels for sacrifice.