Musnad Ahmad 30:1920

'Affan narrated to us, Hammam narrated to us, Qatadah narrated to us, that 'Abd al-Rahman, the freed slave of Umm Burthan, narrated from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Allah prescribed Friday for those who were before us, but they differed concerning it. Then Allah guided us to it. So the people are followers to us regarding it; for the Jews is tomorrow, and for the Christians is the day after tomorrow."