It is narrated from Abu Huraira (may Allah be pleased with him) that he reports from the Prophet (peace and blessings be upon him) that he said: "We are the last to come, but will be the foremost on the Day of Resurrection. The only difference is that the Jews and Christians were given the Book before us and we were given it after them. Then this (Friday) was the day that was made obligatory upon them, but they differed regarding it. So the people (now) follow us in this: Saturday (is for the Jews), Sunday (is for the Christians)."
Hadith Referenceمسند الإمام الشافعي / كتاب الجمعة / 406
Hadith Takhrijاسناده ضعيف لضعف شيخ الشافعي لكن الحديث صحيح اخرجه البيهقي في المعرفة السنن والآثار، رقم : 1660 ۔ واحمد 2 / 502۔