Sunan Abi Dawud 1988
The Rites of Hajj (Kitab Al-Manasik Wa'l-Hajj)
Regarding 'Umrah
AbuBakr ibn AbdurRahman said: The messenger of Marwan whom he sent to Umm Ma'qil reported to me. She said: AbuMa'qil accompanied the Messenger of Allah (ﷺ) during hajj. When he came (to her) she said: You know that hajj is incumbent on me. They walked until they visited him (i.e. the Prophet) and she asked (him): Messenger of Allah, hajj is due from me, and AbuMa'qil has a camel. AbuMa'qil said: She spoke the truth, I have dedicated it to the cause of Allah. The Messenger of Allah (ﷺ) said: Give it to her, that is in the cause of Allah. So he gave the camel to her. She then said: Messenger of Allah, I am a woman who has become aged and ill. Is there any action which would be sufficient for me as my hajj? He replied: umrah performed during Ramadan is sufficient as hajj.