From the beginning of the world to the resurrection of Christ, God appointed the seventh day of the week to be the weekly sabbath; and the first day of the week ever since, to continue to the end of the world, which is the Christian sabbath.1
2 And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made.
3 And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made.
1 Corinthians 16:1-2
1 Now concerning the collection for the saints, as I have given order to the churches of Galatia, even so do ye.
2 Upon the first day of the week let every one of you lay by him in store, as God hath prospered him, that there be no gatherings when I come.
Acts 20:7
7 And upon the first day of the week, when the disciples came together to break bread, Paul preached unto them, ready to depart on the morrow; and continued his speech until midnight.