sabbath day

The best answer i can give you is, in Saudi and most Arab nations, they observe the Sabbath day. On Jumat prayers(fridays) they dont work officially on that day and Saturday. There new week starts on Sunday, that is their work week starts on Sunday as against Monday in other part of the world.

Salam, Friday is The best day of the week. Abu Hurairah reported Allah's Messenger (PBUH) as saying: [ The best day on which the sun has risen is friday...] Narrated by Imam Abu Daud. Friday is The day Allah created Prophet Adam [ ...on it Adam was created,on it he was made to enter Paradise, on it he was expelled from it] Narrated by Imam Abu Daud. On FridayDu’a will be answered. Narrated Abu Hurairah: Allahs Apostle (PBUH) talked about friday and said, [ There is an hour on fridayand if a Muslim gets it while praying...] Narrated by Imam Muslim. [and asks something from Allah, then Allah will definitely meet his demand."] Narrated by Imam Muslim. And about saturday as the rest day of people of Moses (a.s), Allah said in Surat Al A'raf aya 163 [And ask them about the town that was by the sea - when they transgressed in [the matter of] the sabbath - when their fish came to them openly on their sabbath day, and the day they had no sabbath they did not come to them. Thus did We give them trial because they were defiantly disobedient.]. Allah showed us that they used to go fishing on this day. This is according to what I know. Wa Allah a'lam

 Edna. One of the articles of Iman (Islamic faith) is to believe in all Prophets which includes Musa (Mosses) and Issa (Jesus),peace be upon them. Not only to have belief that they are Prophets but also to revere them all. Islamic faith also constitutes another article which is to believe in Holy Books - meaning thereby believing in what(Book) Mosses brought and that which Jesus brought. Please note that ISLAM DOES NOT TELL THE MUSLIMS TO FOLLOW MOSSES AND JESUS, instead, Islamic-teaching is to follow THE LAST OF THE PROPHETS, MUHAMMAD (PEACE BE UPON HIM) AND TO FOLLOW THE BOOK HE BROUGHT, THAT IS QURAN. I would also like you to know that Muhammad (peace be upon him) is the last of the prophets till the end of the world, meaning thereby, that Islam is the final Deen [code of life as prescribed by Allah(God)] for the whole of mankind till the Doomsday.
  About the last part of your question, Jews have Saturdays, christian have Sundays and Muslims have Fridays as the holy days. I would like to tell you that the All-Mighty God had chosen Fridays as the holy days for all the Scripture holders, Jews changed it to Saturday and christian to Sunday. This example alone could stir up one's mind to think what other changes might have been brought about in the previous Commandments of God, by the respective Scripture holders with the passage of time, that necessitated the renewal of God's Commandments, by God, through Prophets after Prophets till the last.  
  You want to know more please feel free to ask.