Al-Jumuah is the most important day of the week for Muslims; just as Shabbat is the most important day of the week for Jews. The importance of jummah for Muslims comes from the Qur’an, chapter 62.
The best day the sun rises over is Friday; on it Allah created Adam. On it, he was made to enter paradise, on it he was expelled from it, and the Last Hour will take place on no other day than Friday.