The difference of the days consecrated to rest and/or the prayer in the Christian, Jewish and Muslim religions are derived from the different tradition from which they draw origin. In reality only within the Jewish culture is there a direct reference to the Biblical text ( Genesis 2, 1-3; Exodus 20, 8-11 and 31, 13 - 17) while the rest coincide with the seventh day of the week, which for the Jewish is Saturday. We do not know precisely, instead, why Sunday became the day for excellence of the Christian liturgy. A theory links the Sunday liturgy to the sabbatical synagogue service, another to the solar cults of the God Mithras, yet a third theory considers Sunday to be a decidedly Christian institution as a weekly commemoration of the Resurrection of Christ. Finally, for the Muslim believers, the day of prayers, actually Friday, is established by the Koran and does not have any reference with the creation.