Sayyiduna Jubayr bin Mut'im (may Allah be pleased with him) narrates: I saw the Prophet (peace and blessings be upon him) on al-Marwah, during his Umrah, trimming his hair, and he (peace and blessings be upon him) was saying: "Umrah has entered into Hajj until the Day of Resurrection. There is no sarurah (abstaining from Hajj)."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 1568