Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: the Messenger of Allah (peace and blessings be upon him) said to a woman of the Ansar: "What prevented you from performing Hajj with us this year?" She said: O Messenger of Allah (peace and blessings be upon him)! My husband and my son rode off on one camel, and only one camel is left, with which we draw water. He (peace and blessings be upon him) said: "Then when Ramadan comes, perform Umrah, for an Umrah in Ramadan is equal to a Hajj."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8742