Q. 64: Which day of the seven has God appointed to be the weekly Sabbath?
A. Before 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.
I was in the Spirit on the Lord’s Day, and I heard behind me a loud voice, as of a trumpet. Revelation 1:10
Now concerning the collection for the saints, as I have given orders to the churches of Galatia, so you must do also: on the first day of the week let each one of you lay something aside, storing up as he may prosper, that there be no collections when I come. 1 Corinthians 16:1-2