Could you please document the New Testament commanding Saturday Sabbath (or any single day of rest) for Christians?
t.y.
Are you kidding? You think the New Testament isn't about the Old? You think Jesus needed to verse by verse repeat them for His audience when He said they would never pass away? If that's your thinking, there's no point in addressing this.
Six days shalt thou labour, and do all thy work:
But the seventh day is the sabbath of the LORD thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates:
For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it. From
Exodus 20
How about you show me anywhere in the NT Christ said that law no longer applies, that it's been dropped or nullified in any way.
You said Christ is our sabbath, which in a manner of speaking is true, but that does not nullify His commandment. Only He has the authority to do that. And He said this commandment is eternal.