Book 20, Number 20.19.67:

Yahya related to me from Malik that Sumayy, the mawla of Abu Bakr ibn Abd ar-Rahman, heard Abu Bakribn Abd ar-Rahman say, "A woman came to 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 the Messenger of Allah, may Allah bless him and grant him peace, said, 'Do umra in Ramadan, for doing umra in it is like doing hajj.' "