Yahya related to me from Malik that Sumayy, the mawla of Abu Bakribn Abd ar-Rahman, heard Abu Bakribn Abd ar-Rahman say, "A woman cameto the Messenger of Allah, may Allah bless him and grant him peace,and said, 'I had arranged to do hajj, but I was prevented,' and theMessenger of Allah, may Allah bless him and grant him peace, said, 'Doumra in Ramadan, for doing umra in it is like doing hajj.' "
USC-MSA web (English) reference: Book 20, Hadith 67
Arabic reference: Book 20, Hadith 771