Sayyiduna Ibn Umar (may Allah be pleased with them both) narrates: the Prophet (peace and blessings be upon him) and his Companions arrived intending Hajj, and he (peace and blessings be upon him) said: "O people, enter ihram for Umrah, except the one who has a sacrificial animal (hady) with him, for Umrah has entered into Hajj until the Day of Resurrection."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13430