Read: Leviticus 23:1-3
There are six days when you may work, but the seventh day is a day of sabbath rest, a day of sacred assembly. You are not to do any work; wherever you live, it is a sabbath to the Lord. Lev 23:3
The weekly sabbath had begun at Creation. God worked six days and then he rested on the seventh day. God did no work on the sabbath. This was reinstated and renewed in the giving of the Law on Mount Sinai when God reminded his people that the sabbath was at the heart of all his work.
I often hear Sunday referred to as the sabbath. And perhaps you think that is just an old-fashioned word for Sunday. But that is completely wrong. Sunday is never the sabbath, and never was the sabbath! A transference is made of these ideas which is totally unbiblical. The seventh day was Saturday. The first day was Sunday. And Saturday was to be observed as the sabbath, as it still is in Israel today.