Musnad Ahmad 30:3592

Uthman ibn Umar narrated to us, Ibn Abi Dhi'b informed us, from Sa'id al-Maqburi, from his father, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The sun has neither risen nor set upon a day better than the day of Friday. Allah has guided us to it, and led people astray from it. So, people are followers to us in it; it is for us, and for the Jews is the day of Saturday, and for the Christians is the day of Sunday. Indeed, there is an hour in it; no believer coincides with it while praying, asking Allah the Mighty and Majestic for something, but He will grant it to him."