A New Sabbath Day?

Some Christians will argue that Sunday is the new Sabbath day. There is however not a single bible verse that confirms that.

It's the opposite in fact.

For if Jesus had given them rest, then would he not afterward have spoken of another day. There remaineth therefore a rest to the people of God. For he that is entered into his rest, he also hath ceased from his own works, as God did from his.
- Hebrews 4:8-10 (KJV)

The word "rest" is sometimes also translated as "Sabbath-rest" (coming from the Greek word sabbatismos).

- Source

God rested on the seventh day, and so should we.

I've seen people that say they keep the Sunday as their Sabbath. Sounds "great", but even then they still don't keep the "no work" part of the commandment. They just do what they want.

Remember the sabbath day, to keep it holy. 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.
- Exodus 20:8-11 (KJV)

Remember that Jesus was quite clear about how the law should be interpreted.

Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil. For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
- Matthew 5:17-18 (KJV)

It's all or nothing!

For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all.
- James 2:10 (KJV)

The Sabbath day (Friday sunset to Saturday sunset) therefore remains.