Musnad Ahmad 30:3485

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