Musnad Abu Ya'la al-Mawsili 161:12

Zuhayr narrated to us, Sufyan narrated to us, Sumayy informed me, from Abu Salih, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), who said: "The accepted Hajj has no reward other than Paradise. And the Umrah to the Umrah, or the two Umrahs, expiate what is between them."