Musnad Ahmad 25:1313

Muhammad ibn Ja‘far and Rawh narrated to us, they said: Shu‘bah narrated to us, from al-Hakam. Rawh said: al-Hakam narrated to us, from Mujahid, from Ibn ‘Abbas, from the Prophet (peace and blessings of Allah be upon him), who said: "This is an ‘Umrah with which we have performed Mut‘ah. So whoever does not have a sacrificial animal (hady) with him, let him exit the state of Ihram completely, for the ‘Umrah has entered into the Hajj until the Day of Resurrection."