Musnad Ahmad 31:626

'Affan narrated to us, he said: Aban narrated to us, Qatadah narrated to us, from 'Abdullah ibn Abi 'Utbah, from Abu Sa'id al-Khudri, from the Prophet (peace and blessings of Allah be upon him), who said: "The House shall surely be performed Hajj to, and it shall surely be performed 'Umrah to, after the emergence of Gog and Magog."