It is narrated from Sayyiduna Yusuf bin Abdullah bin Salam (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said to a man and a woman of the Ansar: "Perform Umrah in the month of Ramadan, for an Umrah in it is equal to a Hajj."
Hadith Referenceالمعجم الكبير للطبراني / باب الياء / 18939