It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "An Umrah in Ramadan is equal to a Hajj." Abu Mu'awiyah added "with me" in his narration (that is: it is equal to a Hajj with me).
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11251