It is narrated from Sayyidah Umm Ma'qil (may Allah be pleased with her) that she asked the Messenger of Allah (peace and blessings be upon him): "What deed is equal to Hajj?" He (peace and blessings be upon him) said: "Umrah in Ramadan is equal to Hajj."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21827