Musnad Ahmad 1248:2

Muhammad ibn Ja‘far and Hajjaj narrated to us, they said: Shu‘bah narrated to us, from Ibrahim ibn Muhajir, from Abu Bakr ibn ‘Abd al-Rahman ibn al-Harith, who said: Marwan sent to Umm Ma‘qil al-Asadiyyah asking her about this hadith, so she narrated to him that her husband had designated a young she-camel of hers for the sake of Allah, and that she wanted to perform ‘Umrah, so she asked her husband for the she-camel, but he refused. She came to the Prophet, peace and blessings of Allah be upon him, and mentioned that to him, so he ordered him to give it to her, and the Prophet, peace and blessings of Allah be upon him, said: "Hajj and ‘Umrah are from the way of Allah." And he said: "An ‘Umrah in Ramadan is equivalent to a Hajj, or suffices for a Hajj." And Hajjaj said: "Equivalent to a Hajj, or suffices for a Hajj."